Diverse Themes
Cyclic Fatty Acids
Taxonomy of Alicyclobacillus
The Function of Hopanoids
Hopene Cyclase and Triterpenes
Doctoral Students

Diverse Themes


I started my scientific career in the lab of Hans Zähner at the University of Tübingen with the elucidation of the action mechanism of the antibiotics borrelidin (a macrolide) and ketomycin (= 3-cyclohexenyl-glyoxylic acid). Borrelidin is a very specific inhibitor of threonyl-tRNA-synthase in eu- and prokaryots. Borreldin-rersistant yeast cells overproduce threonine and homoserine. These mutants possess a feedback-resistant aspartokinase. Ketomycin is converted in Bacillus subtilis by L-leucine dehydrogenase to the corresponding L-amino acid and acts like isoleucine by feedback-inhibition of threonine desaminase. By this mean it induces a deficiency of isoleucine.

To understand the adsorption of bacteria on hydrophobic surfaces as the first step in the formation of biofilms we isolated from natural sources a diversity of bacteria, which stick to teflon tubes. The surprising result was that these bacteria often contain fucose or rhamnose in their outer polysaccharide layer. Both sugars are deoxysugars and introduce hydrophobicity into the polysaccharide.


R. Hütter, K. Poralla , H. G. Zachau, H. Zähner: Über die Wirkungsweise von Borrelidin: Hemmung des Threonineinbaus in sRNA. Biochem. Z. 344, 190-196 (1966)
2. K. Poralla , H. Zähner: Die Hemmung des Einbaus von Threonin in sRNA im zellfreien System und der Synthese von Protein und Nukleinsäuren in der Zelle durch das Antibiotikum Borrelidin. Arch. Mikrobiol. 61, 143-153 (1968)
G. Nass, K. Poralla , H. Zähner: Effect of the antibiotic borrelidin on the regulation of threonine biosynthetic enzymes in E. coli . Biochem.Biophys.Res.Commun. 34, 84-91 (1969)
W.Keller-Schierlein, K. Poralla , H. Zähner: Isolierung, Identifizierung und Wirkungsweise von Ketomycin ((R)-3-Cyclohexenylglyoxylsäure) und dessen Umwandlungsprodukt 3-Cyclohexenylglycin. Arch. Mikrobiol. 67, 339-356 (1969)
K. Poralla : The induction of a dehydrogenase activity for branched chain amino acids in Bacillus subtilis . Arch. Microbiol. 77, 339-343 (1971)
G. Nass, K. Poralla , H. Zähner: Biogenetic amino acid antagonists. Naturwissenschaften 58, 603-610 (1971)
H. Krüpe, K. Poralla : Eigenschaften von Bacillus subtilis Mutanten, die gegen den Isoleucin-Antagonisten Ketomycin resistent sind. Arch. Microbiol. 85, 253-258 (1972)
R. Thiebe, K. Poralla : Origin of the nucleoside Y in yeast tRNA Phe. FEBS Letters 38, 27-28 (1973)
K. Poralla : Borrelidin. In Antibiotics. Mechanism of Action, Herausgeber J. W. Corcoran und F. E. Hahn, Springer-Verlag Berlin-Heidelberg-New York, (1975)
G. Nass, K. Poralla : Genetics of borrelidin resistant mutants of Saccharomyces cerevisiae and properties of their threonyl-tRNA-synthetase. Molec. Gen. Genet. 147, 39-43 (1976)
N. Obermeier, K. Poralla : Some physiological fuctions of the L-leucine dehydrogenase in Bacillus subtilis . Arch. Microbiol. 109, 59-63 (1976)
N. Obermeier, K. Poralla : Experiments on the role of leucine dehydrogenase in initiation of Bacillus subtilis spore germination. FEMS Microbiology Letters 5, 81-83 (1979)
M. Seibold, K.Nill, K. Poralla : Homoserine and threonine pools of borrelidin resistant Saccharomyces cerevisiae mutants with an altered aspartokinase. Arch. Microbiol. 129, 368-370 (1981)
K. Poralla : Reaktionen mit immobilisierten Zellen und Enzymen. Buchkapitel in "Biotechnologie" Metzler-Verlag, Stuttgart 1983
H. E. A. Schenk, K. Poralla , T. Härtner, R. Deimel, D. Thiel: Lipids in Cyanophora paradoxa . I. Unusual fatty acid pattern of Cyanocyta korschikoffiana . Endocyt. C. Res. 2, 233-238 (1985)
D.P. Zook, H. E. A. Schenk, H. G. Frank, D. Thiel, K. Poralla , T. Härtner: Lipids in Cyanophora paradoxa . II. Arachidonic acid in the lipid fractions of the endocyanelle. Endocyt. C. Res. 3, 99-103 (1986)
T.R. Neu, K. Poralla : An amphiphilic polysaccharide from an adhesive Rhodococcus strain. FEMS Microbiol. Lett. 49,389-392 (1988)
T.R. Neu, K. Poralla : Emulsifying agents from bacteria isolated in a screening for cells with hydrophobic surfaces. Appl. Microbiol. Biotechnol. 521-525 (1990)
T.R. Neu, T. Härtner, K. Poralla : Surface active properties of viscosin - a peptidolipid antibiotic. Appl. Microbiol. Biotechnol. 32,518-520 (1990)
P. Bauer, K. Poralla : The polysaccharide capsule and adhesion of Rhodococcus spec .. DECHEMA Biotechnology Conferences Vol. 4,637-640 (1990)
P. Bauer, K. Poralla : Components of the capsule of Rhodococcus spec. and their possible function in adhesion to hydrophobic surfaces. Manuscript verfasst
T.R. Neu, T. Dengler, B. Jann and K. Poralla : Structural studies of an emulsion-stabilizing exopolysaccharide produced by an adhesive, hydrophobic Rhodococcus strain. J. Gen. Microbiology 138, 2531-2537 (1993).
S. Spring, R. Amann, W. Ludwig, K.-H. Schleifer, D. Schüler, K. Poralla , N. Petersen: Phylogenetic analysis of uncultured magnetotactic bacteria from alpha-subclass of Proteobacteria . System. Appl. Microbiol. 17,501-508 (1994)

Cyclic Fatty Acids


Some bacteria contain cyclic fatty acids. Besides the well known cyclopropane fatty acids in Gram-negative bacteria one finds in some Gram-positive bacteria -alicyclic fatty acids.

Alicyclobacillus acidoterrestris and A. acidocaldarius contain
-cyclohexyl fatty acids
and Alicyclobacillus cycloheptanicus
-cycloheptyl fatty acids
. The latter fatty acids were discovered in my lab.

We demonstrated that phospholipids containing these fatty acids form condensed (tight) membranes with an attenuated phase transition. Con-sequently, the neutral cytoplasm of these acidophilic bacteria is sheltered against influx of protons at high growth temperatures.


R. Dreher, K. Poralla , W. A. König: Synthesis of w -alicyclic fatty acids from cyclic precursors in Bacillus subtilis . J. Bacteriol. 127, 1136-1140 (1976)
25. A. Blume, R. Dreher, K. Poralla : The influence of branched-chain and w -aliyclic fatty acids on the transition temperature of Bacillus subtilis lipids. Biochim. Biophys. Acta 512, 489-494 (1978)
B. Hippchen, A. Röll, K. Poralla : Occurrence in soil of thermo-acidophilic bacilli prossessing w -cyclohexane fatty acids and hopanoids. Arch. Microbiol. 129, 53-55 (1981)
K. Poralla , W. A. König: The occurrence of w -cycloheptane fatty acids in a thermo-acidophilic Bacillus. FEMS Microbiol. Letters 16, 303-306 (1983)
R. Benz, D. Hallman, K. Poralla , H. Eibl: Interaction of hopanoids with phosphatidylcholines containing oleic and
-cyclohexyldodecanoic acid in lipid bilayer membranes. Chemistry Physics Lipids 34, 7-24 (1983)
E. Kannenberg, A. Blume, K. Poralla : Properties of
-cyclohexane fatty acids in membranes. FEBS Letters 172, 331-334 (1984)
H. Allgaier, K. Poralla , G. Jung: -Cycloheptyl--hydroxyundecanoic acid, a new fatty acid from a thermo-acidophilic Bacillus species. Liebigs Ann. Chem. 1985, 378-382
E. Kannenberg, A. Blume, K. Geckeler, K. Poralla : Properties of hopanoids and phosphatidylcholine containing
-cyclohexane fatty acids in monolayer and liposome experiments. Biochem. Biophys. Acta 814, 179-185 (1985)
W. Krischke, K. Poralla : Properties of Bacillus acidocaldarius mutants deficient in
-cyclohexyl fatty acid biosynthesis. Arch. Microbiol. 153,463-469 (1990)
H.G. Floss, H. Cho, K.A. Reynolds, E. Kennedy, B.S. Moore, J.M. Beale, U.M. Mocek, K. Poralla : Secondary-Metabolite Biosynthesis and Metabolism. Environmental Science Research (Hrg.: R.J. Petroski und S.P. McCormick) Vol. 44,77-88 (1992)
B.S. Moore, K. Poralla , H.G. Floss: Three new
-cycloheptyl fatty acids from Alicyclobacillus cycloheptanicus and their biosynthestic interrelationship. J. Nat. Products - Lloydia 58,590-593 (1995)
G. Deinhard, K. Poralla : Vorkommen, Biosynthese und Funktion -alicyclischer Fettsäuren bei Bakterien. BIOspektrum 2,40-46 (1996)
B.S. Moore, K. Poralla , H.G. Floss: Biosynthesis of the cyclohexanecarboxylic acid starter unit of -cyclohexyl fatty acids in Alicyclobacillus acidocaldarius. J.Amer.Chem.Soc. 115,5267-5274 (1993).
B.S. Moore, K. Walker, I. Tornus, S. Handa, K. Poralla , H.G. Floss: Biosynthetic studies of -cycloheptyl fatty acids in Alicyclobacillus cycloheptanicus . Formation of Cycloheptanecarboxylic acid from phenylacetic acid. J. Org. Chem. 62,2173-2185 (1997)

Taxonomy of Alicyclobacillus


My group isolated and characterized two new species of thermoacidophilic, aerobic, endopspore forming bacteria from different soil samples. They were named Alicyclobacillus acidoterrestris and Alicyclobacillus cycloheptanicus .

They are occurring in a high variety of different soils. Their titer is 100 – 3000 organisms per g of soil. They contain
-alicyclic fatty acids in high percentage (50 – 90 %)
in their fatty acid pattern. By phylogenetic analysis a wide distance to other Bacillus -species was demonstrated. Therefore, the new genus Alicyclobacilus for this cluster of bacteria was created.

Alicyclobacillus acidoterrestris is meanwhile a well known contaminant of fruit juices and is occurring all over the world. The source of this contaminant are traces of soil in insufficiently pasteurized juices.


B. Hippchen, A. Röll, K. Poralla : Occurrence in soil of thermo-acidophilic Bacilli prossessing -cyclohexane fatty acids and hopanoids. Arch. Microbiol. 129, 53-55 (1981)
39. K. Poralla , W. A. König: The occurrence of -cycloheptane fatty acids in a thermo-acidophilic Bacillus. FEMS Microbiol. Letters 16, 303-306 (1983)
G. Cerny, W. Hennlich, K. Poralla : Fruchtsaftverderb durch Bacillen: Isolierung und Charakterisierung des Verderberregers. Z. Lebens. Unters. Forsch. 179, 224-227 (1984)
H. Allgaier, K. Poralla , G. Jung: -Cycloheptyl-O- hydroxyundecanoic acid, a new fatty acid from a thermo-acidophilic Bacillus species. Liebigs Ann. Chem. 1985, 378-382
G. Deinhard, P. Blanz, K. Poralla , E. Altan: Bacillus acidoterrestris sp.nov ., a new thermotolerant acidophile from different soils. System. Appl. Microbiol. 10,47-53 (1987)
G. Deinhard, J. Saar, W. Krischke, K. Poralla : Bacillus cycloheptanicus sp. nov ., a new thermoacidophile containing -cycloheptane fatty acids. System. Appl. Microbiol. 10,68-73 (1987)
J.D. Wisotzkey, P. Jurthshuk,Jr., G.E. Fox, G. Deinhard, K. Poralla : Comparative sequence analyses on the 16S rRNA (rDNA) of Bacillus acidocaldarius , Bacillus acidoterrestris , and Bacillus cycloheptanicus and proposal for creation of a new genus, Alicyclobacillus gen. nov .. Internat.J.System.Bacteriol. 42,263-269 (1992)

The Function of Hopanoids


(= hopane-22-ol),tetrahydroxybacteriohopane and all other hopanoids with a polar sidechain are constituents of the cytoplasmic membrane in numerous Bacteria ; in Archae they have never been found. Elongated hopanoids like cholesterol condense fatty acid containing lipids in the cytoplasmic membrane. By this condensing effect the lipid phase of a membrane acquires higher viscosity and its barrier function gets more pronounced especially at high growth temperature, low pH, high oxygen tension, or water stress.


K. Poralla , E. Kannenberg, A. Blume: A glycolipid containing hopan isolated from the acidophilic, thermophilic Bacillus acidocaldarius , has a cholesterol-like funktion in membranes. FEBS Letters 113, 107-110 (1980)
46. E. Kannenberg, K. Poralla , A. Blume: A hopanoid from thermoacidophilic Bacillus acidocaldarius condenses membranes. Naturwissenschaften 67, 458-459 (1980)
K. Poralla : Hopanoide-eine Klasse Pentacyclischer Triterpenoide von biologischer und geochemischer Bedeutung. Forum Mikrobiologie 3, 113 (1980)
K. Poralla : Considerations on the evolution of steroids as membrane components. FEMS Microbiol. Letters 13, 131-135 (1982)
K. Poralla : Hopanoide: Steroidäquivalente in Membranen von Bakterien und ein möglicher Seitenzweig bei der Evolution der Steroidbiosynthese. Forum Mikrobiologie 5, 176-179 (1982)
E. Kannenberg, K. Poralla : The influence of hopanoids on growth of Mycoplasma mycoides . Arch. Microbiol. 133, 100-102 (1982)
R. Benz, D. Hallman, K. Poralla , H. Eibl: Interaction of hopanoids with phosphatidylcholines containing oleic and
-cyclohexyldodecanoic acid in lipid bilayer membranes. Chemistry Physics Lipids 34, 7-24 (1983)
E. Kannenberg, A. Blume, R. N. Mc Elhaney, K. Poralla : Monolayer and calorimetric studies of phosphatidylcholines containing branched-chain fatty acids and of their interactions with cholesterol and with a bacterial hopanoid in model membranes. Biochim. Biophys. Acta 733, 111-116 (1983)
K. Poralla , T. Härtner, E. Kannenberg: Effect of temperature and pH on the hopanoid content of Bacillus acidocaldarius . FEMS Microbiol. Lett. 23, 253-256 (1984)
S. Bringer, T. Härtner, K. Poralla , H. Sahm: Influence of ethanol on the hopanoid content and the fatty acid pattern in batch and continuous cultures of Zymomonas mobilis . Arch. Microbiol. 140, 312-316 (1985)
E. Kannenberg, A. Blume, K. Geckeler, K. Poralla : Properties of hopanoids and phosphatidylcholine containing
-cyclohexane fatty acids in monolayer and liposome experiments. Biochem. Biophys. Acta 814, 179-185 (1985)
E. Kannenberg, A. Blume, R. N. McElhaney, K. Poralla : Mixed monolayer studies of the interactions of synthetic phosphatidylcholines containing branched chain fatty acids and hopane glycolipid isolated from thermo-acidophilic bacterium Bacillus acidocaldarius . Chem. Phys. Lipids 39, 145-153 (1986)
A. Schmidt, S. Bringer-Meyer, K. Poralla , H. Sahm: Effect of alcohols and temperature on the hopanoid content of Zymomonas mobilis . Appl. Microb. Biotech. 25, 32-36 (1986)
K. Poralla , E. Kannenberg: Hopanoids - Sterol Equivalents in Bacteria. in "Ecology and Metabolism of Plant Lipids" S. 239-251. Eds: G. Fuller, W. D. Nes, Symposium Series Nr. 325 American Chemical Society, 1987
G. Ourisson, M. Rohmer, K. Poralla : Microbial lipids betrayed by their fossils. Microbiol. Sci. 4, 52-57 (1987)
G. Ourisson, M. Rohmer, K. Poralla : Prokaryotic hopanoids and other polyterpenoid sterol surrogates. Annu. Rev. Microbiol. 41, 301-333 (1987)
G. Kleemann, K. Poralla , G. Englert, H. Kjosen, S. Liaasen-Jensen, S. Neunlist, M. Rohmer: Tetrahymanol from the phototrophic bacterium Rhodopseudomonas palustris : first report of a gammacerane triterpenoid from a prokaryote. J.Gen.Microbiol: 136,2551-2553 (1990)
P. Llopiz, C. Vilcheze, S. Neunlist, K. Poralla , M. Rohmer: Prokaryotic triterpenoids. New hopanoids from the nitrogen fixing bacteria Azotobacter vinelandii, Beijerinckia indica and Beijerinckia mobilis . Microbiology 140,2749-2753 (1994)
G.P.F. Michel, B. Neuß, C.H. Tappe [ doctoral student of the lab of K. Poralla ], J. Baratti: Isolations and characterization of Zymomonas mobilis mutants resistant to octadecyltri-methylammonium chloride, a detergent acting on hopanoid-producing bacteria. Arch.Microbiol. 157,116-124 (1992)
E. Kannenberg, M. Perzl, T. Härtner: The occurrence of hopanoid lipids in Bradyrhizobium . FEMS Microbiol. Letters 127,255-262 (1995). [M. Perzl and T. Härtner are members of the group of K. Poralla )
E.L. Kannenberg, M. Perzl, P. Müller, T. Härtner, K. Poralla : Hopanoid lipids in Bradyrhizobium and other plant assoziated bacteria and cloning of the Bradyrhizobium squalene-hopene cyclase gene. Plant and Soil 186, 107-112 (1996)
J.M. Bravo, M. Perzl, T. Härtner, E.L. Kannenberg, M. Rohmer: Novel methylted triterpenoids of the gammacerane series from the nitrogen-fixing bacterium Bradyrhizobium japonicum USDA 110. Europ. J. Biochem. 268, 1323-1331 (2001); M. Perzl, T. Härtner and E.L. Kannenberg are members of the group of Karl Poralla

Hopene Cyclase and Triterpenes


The crucial reaction of hopanoid biosynthesis is the cyclization of the linear precursor squalene to hopene (= diploptene):

About 30 cyclisation products of squalene and 90 of oxido-squalene are known in higher plants. Consequently more than 100 triterpene cyclases may be postulated. The squalene-hopene cyclase of the bacterium Alicyclobacillus acidocaldarius was the first triterpene cyclase which has been purified, its gene cloned and sequenced. It is also the first triterpene cyclase from which the X-ray structure has been elucidated. By mutation analysis the role of specific amino acid residues has been elaborated.

The main features of the bacterial hopene cyclase are:

1. Side reactions : Besides diplopterol (see in the above scheme) a further pentacyclic triterpene, namely neohop-13(18)-ene, is formed as a minor product. Derivatives of tetracyclic dammarane and 17-isodammarane together with eupha-7,24-diene are also produced.

3. It is a homodimer.

2. It is a monotopic membrane enzyme which dips into the hydrophobic part of the cyctoplasmic membrane.

4. The active site resides in a cavity . A channel connects the cavity to an entrance which is surrounded by hydrophobic amino acids and by these amino acids a connection is formed to the membrane interior where the very hydrophobic squalene is diffusing.

5. To find the entrance, to diffuse into the catalytic cavity and to acquire the afforded conformation is the cause for the low turnover number of 0.3 sec .

6. The reaction is highly exergonic (about 200 kJ/mole). For stabilization of the enzyme the below described QW-motif seems important.

7. The sequence similariy to eukaryotic oxidosqualene cyclases is about 30 %. Besides the overall similarity hopene cyclases have with oxidosqualene cyclases a non-tandem repeat motif in common. Its consensus sequence is:
Arg/Lys Ala/Gly X X Phe/Tyr/Trp Leu X X X Gln X X X Gly X Try .
Because of the most conserved residues (Gln=Q, Trp=W) it was named QW-motif .

8. Besides this repeat motif an Asp (D) containing motif is located at homologous position. In hopene cyclases the sequence is DXDDTA and in oxidosqualene cyclases XXDCTA. The Asp residues are the proton donating residues in the cyclization reaction.

9. Aromatic amino acids are essential in the stabilization of cationic intermediates and influence the specificity of the reaction and

10. The introduction of Lys at critical points leads to the creation of “new” cyclases synthesizing products with 2 and 4 rings.

My work on triterpenes and hopanoids is connected by cooperation and friendship to Guy Ourisson and Michel Rohmer.


B. Seckler, K. Poralla : Characterization and partial purification of squalen-hopene cyclase from Bacillus acidocaldarius . Biochim. Biophys. Acta 881, 356-363 (1986)
68. J. Saar: Reinigung und Charakterisierung der Squalen-Tetrahymanol-Cyclase des Ciliaten Tetrahymena thermophila . Dissertation, Universität Tübingen 1989 [in cooperation with Guy Ourisson]
A. Schmidt, S. Bringer-Meyer, K. Poralla , H. Sahm: Influence of ethanol on the activities of 3-hydroxy-3-methylglutaryl-coenzyme A-reductase and squalene-hopene cyclase in Zymomonas mobilis . Appl.Microbiol.Biotechnol. 32,521-525 (1990)
D. Ochs, R. Kellner, K. Poralla : Properties of purified squalene-hopene cyclase from Bacillus acidocaldarius . Europ.J.Biochem. 194,75-80 (1990)
J. Saar, J.-C. Kader, K. Poralla , G. Ourisson: Purification and some properties of the squalene-tetrahymanol cyclase from Tetrahymena thermophila. Biochim.Biophys.Acta 1075,93-101 (1991)
D. Ochs, C. Kaletta, K.-D. Entian, A. Beck-Sickinger, K. Poralla : Cloning, expression, and sequencing of squalene-hopene cyclase, a key enzyme in triterpenoid metabolism. J.Bacteriol. 174,298-302 (1992)
K. Poralla : The possible role of a repetitive amino acid motif in evolution of triterpenoid cyclases. Bioorganic Medicinal Chemistry Letters 4, 285-290 (1994).
G. Kleemann, K. Poralla : Purification and properties of the squalene-hopene cyclase from Rhodopseudomonas palustris , a purple non-sulfur bacterium producing hopanoids and tetrahymanol. Biochim. Biophys. Acta 1210, 317-320 (1994).
K. Poralla , A. Hewelt, G.D. Prestwich, I. Abe, I. Reipen, G. Sprenger: A specific amino acid motif in squalene and oxidosqualene cyclases. Trends in Biochemical Sciences 19, 157-158 (1994). - About the QW -motif.
Wieland, C. Feil, E.-G. Maercker, G. Thumm, M. Lechner, J.-M. Bravo, K. Poralla and F. Götz: Genetic analysis of the biosynthesis of the yellow carotenoid 4,4'-diaponeurosporene of Staphylococcus aureus . J. Bacteriol. 176, 7719-7726 (1994)
I.G. Reipen, K. Poralla , H. Sahm, G.A. Sprenger: Cloning, DNA sequence analysis, and expression in Escherichia coli K-12 of the Zymomonas mobilis shc gene encoding squalene-hopene cyclase. Microbiology 141, 155-161 (1995)
C. Feil, R. Süssmuth, G. Jung. K. Poralla : Squalene-hopene cyclase: Site-directed mutagenesis of putative active-site residues. Europ.J.Biochem. 242,51-55 (1996)
M. Perzl, P. Müller, K. Poralla , E.L. Kannenberg: Squalene-hopene cyclase from Bradyrhizobium japonicum : cloning, expression, sequence analysis and comparison to other triterpenoid cyclases. Microbiology 143,1235-1242 (1997)
U. Wendt, C. Feil, A. Lenhart, K. Poralla , G.E. Schulz: Crystallisation and preliminary X-ray crystallographic analysis of squalene-hopene cyclase from Alicyclobacillus acidocaldarius . Protein Sci. 6,722-724 (1997)
U. Wendt, K. Poralla , G.E. Schulz: Structure and function of a squalene cyclase. Science 277, 1811-1815 (1997). – This paper has been cited 120 times until August 2003.
I. Abe, T. Dang, Y.F. Zheng, B.A. Madden, C. Feil,
K. Poralla
, G.D. Prestwich: Cyclization of
(3S)29-methylidene-2,3-oxidosqualene by bacterial squalene:hopene cyclase: Irreversible enzyme inactivation and isolation of an unnatural dammarenoid. J. Am. Chem. Soc. 119, 11333-11334 (1997).
A. Tippelt, L. Jahnke, K. Poralla : Squalene-hopene cyclase from Methylococcus capsulatus (Bath): a bacterium producing hopanoids and steroids. Biochim. Biophys. Acta 1391, 223-232 (1998)
C. Pale-Grosdemange, C. Feil, M. Rohmer, K. Poralla : Kationische Zwischenstufen und fehlerhafte Kontrolle während der enzymatischen Cyclisierung von Squalen zu Hopanoiden. Angewandte Chemie 110, 2355-2358 (1998)
C. Pale-Grosdemange, C. Feil, M. Rohmer, K. Poralla : Occurrence of cationic intermediates and deficient control during enzymatic cyclization of squalene into hopanoids. Angewandte Chemie (International Edition) 37, 2237-2240 (1998)
M. Perzl, I.G. Reipen, S. Schmitz, K. Poralla , H. Sahm, G.A. Sprenger,E.L. Kannenberg: Cloning of conserved genes from Zymomnas mobilis and Bradyrhizobium japonicum that function in the biosynthesis of hopanoid lipids. Biochim. Biophys. Acta 1393, 108-118 (1998)
K. Poralla : Die Struktur der Squalen-Hopen-Cyclase. BIOspektrum 4, 32-34 (1998)
Review: K. Poralla : Cycloartenol and Triterpene Cyclases. in Comprehensive Natural Products Chemistry . Elsevier, Amsterdam; eds. D. Barton und K. Nakanishi; Vol. 2, 299-319 (1999)
Review: E.L. Kannenberg, K. Poralla : Hopanoid biosynthesis and function in bacteria. Naturwissenschaften 86, 168-176 (1999).
T. Merkofer, C. Pale-Grosdemange, K.U. Wendt, M. Rohmer, K. Poralla : Altered product pattern of a squalene-hopene cyclase by mutagenesis of active site residues. Tetrahedron Letters 40, 2121-2124 (1999).
C. Pale-Grosdemange, T. Merkofer, M. Rohmer, K. Poralla : Production of bicyclic and tricyclic triterpenes by mutated squalene-hopene cyclase. Tetrahedron Letters 40, 6009-6012 (1999)
E.L. Kannenberg, T. Härtner, M. Perzl, S. Schmitz,
K. Poralla
: Hopanoid lipid content of Bradyrhizobium bacteria is dependent on culture conditions. In „Highlights of Nitrogen Research“ eds E. Martínez and G. Herández, Kluwer Academic/Plenum Publishers, New York 1999
C. Füll, K. Poralla : Conserved Tyr residues determine functions of Alicyclobacillus acidocaldarius squalene-hopene cyclase. FEMS Microbiol. Lett. 183, 221-224 (2000)
K. Poralla , G. Muth, T. Härtner: Hopanoids are formed during transition from substrate to aerial hyphae in Streptomyces coelicolor A3(2). FEMS Microbiol. Lett. 189, 93-95 (2000).
F. Viola, M. Ceruti, L. Cattel, P. Milla, K. Poralla , G. Balliano: Rationally designed inhibitors as tools for comparing the mechanism of squalene-hopene cyclase with oxidosqualene cyclase. Lipids 35, 297 – 303 (2000)
S. Schmitz, C. Füll, T. Glaser, K. Albrecht, K. Poralla : Specific production of g -polypodatetraene or 17-isodammara-20(21)-24-diene by squalene-hopene cyclase mutants. Tetrahedron Letters 42, 883-885 (2001)
K. Poralla : The changing path of hopanoid research: From condensing lipids to new membrane enzymes. p. 263-284 in The Microbial Fundamentals of Biotechnologgy; Eds. V. Braun and F. Götz; Wiley-VCH 2001
C. Füll [ former doctoral student of the lab of K. Poralla ]: Bicyclic triterpenes as new main products of squalene-hopene cyclase by mutation at conserved tyrosine residues. FEBS Letters 509, 361-364 (2001).

Doctoral Students

1. Norbert Obermeier 12. Dietmar Ochs
2. Renate Dreher 13. Corinna Feil
3. Elmar Kannenberg 14. Michael Perzl
4. Thomas Neu 15. Ok-Byung Choi
5. Wolfgang Krischke 16. Anette Tippelt
6. Gabriele Deinhard 17. Gabriele Schaule
7. Jörg Saar 18. Nicole Karafyllis
8. Brigitte Seckler 19. Susanne Schmitz
9. Petra Bauer 20. Christine Füll
10. Gisela Kleemann 21. Thorsten Merkofer
11. Cord Tappe 22. Michael Knigge

A special acknowledgment deserves my excellent technician
for many years Thomas Härtner