Characterization of a Pseudomonas putida Allylic Alcohol Dehydrogenase Induced by Growth on 2-Methyl-3-Buten-2-ol

We have been working to develop an enzymatic assay for the alcohol 2-methyl-3-buten-2-ol (232-MB), which is produced and emitted by certain pines. To this end we have isolated the soil bacterium Pseudomonas putida MB-1, which uses 232-MB as a sole carbon source. Strain MB-1 contains inducible 3-methyl-2-buten-1-ol (321-MB) and 3-methyl-2-buten-1-al dehydrogenases, suggesting that 232-MB is metabolized by isomerization to 321-MB followed by oxidation. 321-MB dehydrogenase was purified to near-homogeneity and found to be a tetramer (151 kDa) with a subunit mass of 37,700 Da. It catalyzes NAD⁺-dependent, reversible oxidation of 321-MB to 3-methyl-2-buten-1-al. The optimum pH for the oxidation reaction was 10.0, while that for the reduction reaction was 5.4. 321-MB dehydrogenase oxidized a wide variety of aliphatic and aromatic alcohols but exhibited the highest catalytic specificity with allylic or benzylic substrates, including 321-MB, 3-chloro-2-buten-1-ol, and 3-aminobenzyl alcohol. The N-terminal sequence of the enzyme contained a region of 64% identity with the TOL plasmid-encoded benzyl alcohol dehydrogenase of P. putida. The latter enzyme and the chromosomally encoded benzyl alcohol dehydrogenase of Acinetobacter calcoaceticus were also found to catalyze 321-MB oxidation. These findings suggest that 321-MB dehydrogenase and other bacterial benzyl alcohol dehydrogenases are broad-specificity allylic and benzylic alcohol dehydrogenases that, in conjunction with a 232-MB isomerase, might be useful in an enzyme-linked assay for 232-MB.     

Comparison of substrate specificity of alcohol dehydrogenases from human liver, horse liver, and yeast towards saturated and 2-enoic alcohols and aldehydes

The saturated and 2-enoic primary alcohols and aldehydes, ethanol, 1-propanol, 1-butanol, 3-methyl-1-butanol, 1-hexanol, phenylmethanol, 3-phenyl-1-propanol, 2-propen-1-ol, 2-buten-1-ol, 3-methyl-2-buten-1-ol, 2-hexen-1-ol, 3-phenyl-2-propen-1-ol, ethanal, 1-propanal, 1-butanal, 1-hexanal, phenylmethanal, 3-phenyl-1-propanal, 2-propen-1-al, 2-buten-1-al, 2-hexen-1-al, and 3-phenyl-2-propen-1-al, have been compared under uniform conditions as substrates for the alcohol dehydrogenase enzymes from horse and human liver and from yeast. Kinetic constants (K_m arid V) have been measured for each of the substrates with each of the enzymes; equilibrium constants for the various alcohol-aldehyde pairs have also been estimated. The results obtained emphasize the similarities of yeast alcohol dehydrogenase to horse and human liver alcohol dehydrogenase, showing the specificity of yeast alcohol dehydrogenase to be less restricted than formerly believed. In general, the 2-enoic alcohols are better substrates for all three alcohol dehydrogenases than their saturated analogs; on the other hand, saturated aldehydes are better substrates than the 2-enoic aldehydes. Based on these various findings, it is suggested that a more likely candidate than ethanol for the physiological substrate of alcohol dehydrogenase in mammalian systems may well be an unsaturated alcohol, although the wide variety of substrates catalyzed at high rates is not incompatible with a general detoxifying function for alcohols or aldehydes, or both, by alcohol dehydrogenase.     

Engineering an Isoprenoid Pathway in Escherichia coli for Production of 2-Methyl-3-buten-2-ol: A Potential Biofuel

2-Methyl-3-buten-2-ol (MBO) is a natural volatile 5-carbon alcohol produced by several pine species that have the potential to be used as biofuel. MBO has a high energy content making it superior to ethanol in terms of energy output, and due to its volatility and lower solubility in water, MBO is easier to recover than ethanol. Pine’s MBO synthase enzyme utilizes the intermediate dimethylallyl pyrophosphate (DMAPP) produced by the methyl-erythritol-4-phosphate isoprenoid pathway for the production of MBO. In this study, we performed metabolic engineering of Escherichia coli to express an alternate mevalonate dependent pathway for production of DMAPP, along with a codon optimized Pinus sabiniana MBO synthase gene. This heterologous expressed pathway carried out the conversion of an acetyl CoA precursor to DMAPP leading to production of MBO.     

Host resistance elicited by methyl jasmonate reduces emission of aggregation pheromones by the spruce bark beetle, Ips typographus

We treated Norway spruce (Picea abies) stems with methyl jasmonate (MeJA) to determine possible quantitative and qualitative effects of induced tree defenses on pheromone emission by the spruce bark beetle Ips typographus. We measured the amounts of 2-methyl-3-buten-2-ol and (S)-cis-verbenol, the two main components of the beetle's aggregation pheromone, released from beetle entrance holes, along with phloem terpene content and beetle performance in MeJA-treated and untreated Norway spruce logs. As expected, phloem terpene levels were higher and beetle tunnel length was shorter (an indication of poor performance) in MeJA-treated logs relative to untreated logs. Parallel to the higher phloem terpene content and poorer beetle performance, beetles in MeJA-treated logs released significantly less 2-methyl-3-buten-2-ol and (S)-cis-verbenol, and the ratio between the two pheromone components was significantly altered. These results suggest that host resistance elicited by MeJA application reduces pheromone emission by I. typographus and alters the critical ratio between the two main pheromone components needed to elicit aggregation. The results also provide a mechanistic explanation for the reduced performance and attractivity observed in earlier studies when bark beetles colonize trees with elicited host defenses, and extend our understanding of the ecological functions of conifer resistance against bark beetles.     

Characterization of a Pseudomonas putida allylic alcohol dehydrogenase induced by growth on 2-methyl-3-buten-2-ol.

We have been working to develop an enzymatic assay for the alcohol 2-methyl-3-buten-2-ol (232-MB), which is produced and emitted by certain pines. To this end we have isolated the soil bacterium Pseudomonas putida MB-1, which uses 232-MB as a sole carbon source. Strain MB-1 contains inducible 3-methyl-2-buten-1-ol (321-MB) and 3-methyl-2-buten-1-al dehydrogenases, suggesting that 232-MB is metabolized by isomerization to 321-MB followed by oxidation. 321-MB dehydrogenase was purified to near-homogeneity and found to be a tetramer (151 kDa) with a subunit mass of 37,700 Da. It catalyzes NAD+-dependent, reversible oxidation of 321-MB to 3-methyl-2-buten-1-al. The optimum pH for the oxidation reaction was 10.0, while that for the reduction reaction was 5.4. 321-MB dehydrogenase oxidized a wide variety of aliphatic and aromatic alcohols but exhibited the highest catalytic specificity with allylic or benzylic substrates, including 321-MB, 3-chloro-2-buten-1-ol, and 3-aminobenzyl alcohol. The N-terminal sequence of the enzyme contained a region of 64% identity with the TOL plasmid-encoded benzyl alcohol dehydrogenase of P. putida. The latter enzyme and the chromosomally encoded benzyl alcohol dehydrogenase of Acinetobacter calcoaceticus were also found to catalyze 321-MB oxidation. These findings suggest that 321-MB dehydrogenase and other bacterial benzyl alcohol dehydrogenases are broad-specificity allylic and benzylic alcohol dehydrogenases that, in conjunction with a 232-MB isomerase, might be useful in an enzyme-linked assay for 232-MB.     

High-throughput enzyme screening platform for the IPP-bypass mevalonate pathway for isopentenol production

Isopentenol (or isoprenol, 3-methyl-3-buten-1-ol) is a drop-in biofuel and a precursor for commodity chemicals such as isoprene. Biological production of isopentenol via the mevalonate pathway has been optimized extensively in Escherichia coli, yielding 70% of its theoretical maximum. However, high ATP requirements and isopentenyl diphosphate (IPP) toxicity pose immediate challenges for engineering bacterial strains to overproduce commodities utilizing IPP as an intermediate. To overcome these limitations, we developed an “IPP-bypass” isopentenol pathway using the promiscuous activity of a mevalonate diphosphate decarboxylase (PMD) and demonstrated improved performance under aeration-limited conditions. However, relatively low activity of PMD toward the non-native substrate (mevalonate monophosphate, MVAP) was shown to limit flux through this new pathway. By inhibiting all IPP production from the endogenous non-mevalonate pathway, we developed a high-throughput screening platform that correlated promiscuous PMD activity toward MVAP with cellular growth. Successful identification of mutants that altered PMD activity demonstrated the sensitivity and specificity of the screening platform. Strains with evolved PMD mutants and the novel IPP-bypass pathway increased titers up to 2.4-fold. Further enzymatic characterization of the evolved PMD variants suggested that higher isopentenol titers could be achieved either by altering residues directly interacting with substrate and cofactor or by altering residues on nearby α-helices. These altered residues could facilitate the production of isopentenol by tuning either k_cat or K_i of PMD for the non-native substrate. The synergistic modification made on PMD for the IPP-bypass mevalonate pathway is expected to significantly facilitate the industrial scale production of isopentenol.     

Chemical composition of the essential oils of two Rhodiola species from Tibet

The essential oils from rhizomes of Rhodiola crenulata and R. fastigiata in eastern Tibet were analyzed by using GC-MS. The major constituents were geraniol (53.3%), n-octanol (13.4%), 2-methyl-3-buten-2-ol (10.8%), citronellol (5.3%), 3-methyl-2-buten-1-ol (4.0%), myteol (3.0%), and linalool (2.4%) for R. crenulata and geraniol (45.3%), n-octanol (12.3%), 2-methyl-3-buten-2-ol (8.0%), linalool (5.1%), isogeraniol (4.5%), citronellol (4.4%), and cis-sabinenehydrate (3.6%) for R. fastigiata.     

Incorporation of methionine-[methyl-2H3] and mevalonic acid-[2-14C,(4R)-4-3H1] into Phycomyces blakesleeanus sterols

Ergosterol, episterol, 4α-methyl-5α-ergosta-8,24(28)-dien-3β-ol and 24-methylene-24,25-dihydrolanosterol, isolated from Phycomyces blakesleeanus grown in the presence of methionine-[methyl-²H₃], each contained two deuterium atoms; lanosterol, however, was unlabelled. The ¹⁴C:³H atomic ratio of the following sterols isolated from P. blakesleeanus grown in the presence of mevalonic acid-[2-¹⁴C,(4R)-4-³H₁], was: ergosterol, 5:3; episterol, 5:4; ergosta-5,7,24(28)-trien-3β-ol, 5:3; 4α-methyl-5α-ergosta-8,24(28)-dien-3β-ol, 5:4; 24-methylene-24,25-dihydrolanosterol, 6:5; lanosterol, 6:5. The significance of these results in terms of ergosterol biosynthesis is discussed.     

Acid-catalyzed formation of isoprene from a mevalonate-derived product using a rat liver cytosolic fraction

Isoprene formation in a rat liver cytosolic fraction is shown to be increased 146-fold by acid treatment. This acid catalysis is dependent upon prior incubation of the cytosolic fraction with DL-mevalonate and is stimulated when the incubation also contains ATP. Formation of isoprene proceeds linearly through 5 h of acid treatment and is nearly complete at 10 h. These results suggest that the acid-catalyzed isoprene formation arises from the decomposition of dimethylallyl pyrophosphate via a carbonium ion mechanism. Chemical model studies using 3-methyl-2-buten-1-ol and 3-methyl-3-buten-1-ol (the alcohols corresponding to dimethylallyl pyrophosphate and isopentenyl pyrophosphate, respectively) confirm this hypothesis. At a pH less than or equal to 1, an 85% decomposition of 3-methyl-2-buten-1-ol to isoprene occurred after 24 h, while 3% of 3-methyl-3-buten-1-ol was converted to isoprene under identical conditions and time. It is concluded that the predominant immediate precursor of isoprene is dimethylallyl pyrophosphate and at low pH the ultimate fate of dimethylallyl pyrophosphate is complete conversion to isoprene. These conclusions have important biochemical and methodological implications.     

Behavioural and electrophysiological responses of the bark beetle, Ips typographus, to potential pheromone components

ABSTRACT. Field tests showed ( S )-(-)- cis -verbenol and ( R )-(+)- trans -verbenol in combination with a second pheromonal component, 2-methyl-3-buten-2-ol, more attractive than the combination with their optical antipodes. Inhibition of response to the attractant component, ( S )-(-)- cis -verbenol, by high concentrations of its optical antipode did not occur. No significant differences were noted for response to the attractant, ( S )-(-)- cis -verbenol and 2-methyl-3-buten-2-ol, with the addition of either ipsdienol enantiomer or a racemic mixture of ipsdienol enantiomers. Electroantennogram (EAG) studies correlated well with the behavioural studies. EAGs recorded from male and female beetles revealed both sexes to have a lower threshold for the pheromone, ( S )-(-)- cis -verbenol, than its host terpene precursor, (-)- alpha -pinene. EAGs showed a greater number of acceptors for (-)- alpha-pinene in males than in females. EAGs at acceptor saturation to the enantiomers of alpha -pinene and the verbenol isomers showed males more responsive to (-)- alpha -pinene, (±)- cis -verbenol, and ( R )-(+)- trans -verbenol. Significantly greater EAGs were elicited in females than in males to (-)- alpha -pinene, and (±)- and ( S )-(-)- cis -verbenol. No significant differences in EAGs of females to the enantiomers of trans -verbenol were noted. EAGs showed similar thresholds in males and females to the pheromone component, 2-methyl-3-buten-2-ol; however, female response at threshold was significantly greater than male response. The results are discussed with regard to olfactory acceptor evolution.     

Bacterial degradation of tert-amyl alcohol proceeds via hemiterpene 2-methyl-3-buten-2-ol by employing the tertiary alcohol desaturase function of the Rieske nonheme mononuclear iron oxygenase MdpJ

Tertiary alcohols, such as tert-butyl alcohol (TBA) and tert-amyl alcohol (TAA) and higher homologues, are only slowly degraded microbially. The conversion of TBA seems to proceed via hydroxylation to 2-methylpropan-1,2-diol, which is further oxidized to 2-hydroxyisobutyric acid. By analogy, a branched pathway is expected for the degradation of TAA, as this molecule possesses several potential hydroxylation sites. In Aquincola tertiaricarbonis L108 and Methylibium petroleiphilum PM1, a likely candidate catalyst for hydroxylations is the putative tertiary alcohol monooxygenase MdpJ. However, by comparing metabolite accumulations in wild-type strains of L108 and PM1 and in two mdpJ knockout mutants of strain L108, we could clearly show that MdpJ is not hydroxylating TAA to diols but functions as a desaturase, resulting in the formation of the hemiterpene 2-methyl-3-buten-2-ol. The latter is further processed via the hemiterpenes prenol, prenal, and 3-methylcrotonic acid. Likewise, 3-methyl-3-pentanol is degraded via 3-methyl-1-penten-3-ol. Wild-type strain L108 and mdpJ knockout mutants formed isoamylene and isoprene from TAA and 2-methyl-3-buten-2-ol, respectively. It is likely that this dehydratase activity is catalyzed by a not-yet-characterized enzyme postulated for the isomerization of 2-methyl-3-buten-2-ol and prenol. The vitamin requirements of strain L108 growing on TAA and the occurrence of 3-methylcrotonic acid as a metabolite indicate that TAA and hemiterpene degradation are linked with the catabolic route of the amino acid leucine, including an involvement of the biotin-dependent 3-methylcrotonyl coenzyme A (3-methylcrotonyl-CoA) carboxylase LiuBD. Evolutionary aspects of favored desaturase versus hydroxylation pathways for TAA conversion and the possible role of MdpJ in the degradation of higher tertiary alcohols are discussed.     

The role of semiochemicals in tritrophic interactions between the spruce bark beetle Ips typographus, its predators and infested spruce

Abstract:  Semiochemical interactions between the spruce bark beetle Ips typographus , its predators Medetera setiventris , Thanasimus formicarius and Thanasimus femoralis , and the host Norway spruce, Picea abies , were studied in the field. The chemicals S - cis -verbenol, 2-methyl-3-buten-2-ol, ipsdienol, (+)- α -pinene, (−)- α -pinene, (±)- α -pinene, limonene, camphor and their naturally occuring mixtures were used as trap baits in a multiple-choice design that allowed for comparison of their attractivity for the focal species. Medetera was attracted to both the prey aggregation pheromone and its multifunctional component, ipsdienol. On the contrary, both Thanasimus species responded predominantly to ipsdienol and less to the prey aggregation pheromone. In the case of I. typographus , the attractivity of aggregation pheromone seems to be increased by the addition of a mixture of monoterpenic tree volatiles, and by addition of ipsdienol. Bark beetles and predators showed species-specific responses to volatile mixtures representing different stages of tree decay and different stages of bark beetle colony establishment. These responses correlates with the optimal foraging habitat of each species. None of the predator species responded to 2-methyl-3-buten-2-ol, a substantial component of I. typographus pheromonal bouquet, thus it is hypothesized that only substances of monoterpenic origin attract predators.     

Synthesis of Short-Chain Diols and Unsaturated Alcohols from Secondary Alcohol Substrates by the Rieske Nonheme Mononuclear Iron Oxygenase MdpJ

The Rieske nonheme mononuclear iron oxygenase MdpJ of the fuel oxygenate-degrading bacterial strain Aquincola tertiaricarbonis L108 has been described to attack short-chain tertiary alcohols via hydroxylation and desaturation reactions. Here, we demonstrate that also short-chain secondary alcohols can be transformed by MdpJ. Wild-type cells of strain L108 converted 2-propanol and 2-butanol to 1,2-propanediol and 3-buten-2-ol, respectively, whereas an mdpJ knockout mutant did not show such activity. In addition, wild-type cells converted 3-methyl-2-butanol and 3-pentanol to the corresponding desaturation products 3-methyl-3-buten-2-ol and 1-penten-3-ol, respectively. The enzymatic hydroxylation of 2-propanol resulted in an enantiomeric excess of about 70% for the (R)-enantiomer, indicating that this reaction was favored. Likewise, desaturation of (R)-2-butanol to 3-buten-2-ol was about 2.3-fold faster than conversion of the (S)-enantiomer. The biotechnological potential of MdpJ for the synthesis of enantiopure short-chain alcohols and diols as building block chemicals is discussed.     

Methane monooxygenase catalyzed oxygenation of 1,1-dimethylcyclopropane. Evidence for radical and carbocationic intermediates

Methane monooxygenase catalyzes the oxygenation of 1,1-dimethylcyclopropane in the presence of O2 and NADH to (1-methylcyclopropyl)methanol (81%), 3-methyl-3-buten-1-ol (6%), and 1-methyl-cyclobutanol (13%). Oxygenation by 18O2 using the purified enzyme proceeds with incorporation of 18O into the products. Inasmuch as methane monooxygenase catalyzes the insertion of O from O2 into a carbon-hydrogen bond of alkanes, (1-methylcyclopropyl)methanol appears to be a conventional oxygenation product. 3-Methyl-3-buten-1-ol is a rearrangement product that can be rationalized on the basis that enzymatic oxygenation of 1,1-dimethylcyclopropane proceeds via the (1-methylcyclopropyl)carbinyl radical, which is expected to undergo rearrangement with ring opening to the homoallylic 3-methyl-3-buten-1-yl radical in competition with conventional oxygenation. Oxygenation of the latter radical gives 3-methyl-3-buten-1-ol. 1-Methylcyclobutanol is a ring-expansion product, whose formation is best explained on the basis that the 1-methylcyclobutyl tertiary carbocation is an oxygenation intermediate. This cation would result from rearrangements of carbocations derived by one-electron oxidation of either radical intermediate. The fact that both 3-methyl-3-buten-1-ol and 1-methylcyclobutanol are produced suggests that the oxygenation mechanism involves both radical and carbocationic intermediates. Radicals and carbocations can both be intermediates if they are connected by an electron-transfer step. A reasonable reaction sequence is one in which the cofactor (mu-oxo)diiron reacts with O2 and two electrons to generate a hydrogen atom abstracting species and an oxidizing agent. The hydrogen-abstracting species might be the enzymic radical or another species generated by the iron complex and O2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biosynthesis of 1α,2α,3β-trihydroxy-p-menthane by Fusicoccum amygdali

Measurement of isotope ratios in 1α,2α,3β-trihydroxy-p-menthane, which has been biosynthesized in Fusicoccum amygdali from ³H- and ¹⁴C-labelled mevalonate and in its degradation product diosphenol indicates that: (a) four tritium atoms arising from [5-³H₂, 2-¹⁴C]MVA are retained, one more than suggested from the hydroxylation pattern, (b) menth-2-ene-1-ol is generated from an α-terpinyl cation through a 1,3-hydride shift and (c) trans-cleavage of an α-epoxide by hydrolysis gives 1α,2α,3β-trihydroxy-p-menthane.     

Sterols with unusual nuclear unsaturation from three cultured marine dinoflagellates

Several new 4α-methyl sterols with unusual unsaturation in the Δ⁸⁽¹⁴⁾-or Δ¹⁴-positions, 4α,24S-dimethyl-5α-cholest-8 (14)-en-3β-ol, 4α-methyl-24ξ-ethyl-5α-cholest-8(14)-en-3β-ol, 4α-methyl-24(Z)-ethylidene-5α-cholest-8(14)- en-3β-ol, 4α,23 (or 22),24ξ-trimethyl-5α-cholesta-8(14),22-dien-3β-ol, 4α,24S(or 23ξ)-dimethyl-5α-cholest-14-en-3β-ol and 14-dehydrodinosterol, have been isolated from extracts of the cultured marine dinoflagellates Amphidinium carterae, A. corpulentum and Glenodinium sp. 4α-Methyl-24ξ-ethyl-5α-cholestan-3β-ol was isolated from the steryl ester fraction of Glenodinium sp. The structures of these new sterols are based upon extensive 360 MHz ¹H NMR and MS analyses.     

Sulcatol: population aggregation pheromone in the scolytid beetle, Gnathotrichus sulcatus

The population aggregation pheromone produced by males of Gnathotrichus sulcatus, a timber pest, has been identified from boring dust as a $\text{65}\text{35}$ mixture of the (S)-(+) and the (R)-(?) enantiomers of 6-methyl-5-hepten-2-ol. In field studies beetles were attracted in a 2·65 female: 1 male ratio by racemic synthetic pheromone.     

Metabolism of kaurenoids by Gibberella fujikuroi in the presence of the plant growth retardant,N,N,N-trimethyl-1-methyl-(2′,6′,6′-trimethylcyclohex-2′-en-1′-yl)prop-2-enylammonium iodide

The plant growth retardant, N,N,N-trimethyl-1-methyl-(2′,6′,6′-trimethylcyclohex-2′-en-1′-yl)prop-2-enylammonium iodide, is shown to block gibberellin biosynthesis in Gibberella fujikuroi between mevalonate and ent-kaur-16-ene, probably by inhibiting ent-kaur-16-ene synthetase A-activity. In the presence of the plant growth retardant, cultures of the fungus incorporate (26.5%) added ent-[¹⁴C]-kaur-16-ene into gibberellin A₃. Under the same conditions kaur-16-ene, 13β-kaur-16-ene, and ent-kaur-15-ene are not metabolised to gibberellin analogues.     

Effect of ay-9944 on sterol biosynthesis in Chlorella sorokiniana

When Chlorella sorokiniana was grown in the presence of 4 ppm AY-9944 total sterol production was unaltered in comparison to control cultures. However, inhibition of sterol biosynthesis was shown by the accumulation of a number of sterols which were considered to be intermediates in sterol biosynthesis. The sterols which were found in treated cultures were identified as cyclolaudenol, 4α,14α-dimethyl-9β,19-cyclo-5α-ergost-25-en-3β-ol, 4α,14α-dimethyl -5α-ergosta-8,25-dien-3β-ol, 14α-methyl-9β,19-cyclo-5α-ergost-25-en-3β-ol, 24-methylpollinastanol, 14α-methyl-5α-ergost-8-en-3β-ol, 5α-ergost -8(14)-enol, 5α-ergost-8-enol, 5α-ergosta-8(14),22-dienol, 5α-ergosta-8,22-dienol, 5α-ergosta-8,14-dienol, and 5α-ergosta-7,22-dienol, in addition to the normally occurring sterols which are ergosterol, 5α-ergost-7-enol, and ergosta-5,7-dienol.The occurrence of these sterols in the treated culture indicates that AY-9944 is an effective inhibitor of the Δ⁸ → Δ⁷ isomerase and Δ¹⁴-reductase, and also inhibits introduction of the Δ²²-double bond. The occurrence of 14α-dimethyl-5α-ergosta-8,25-dien-3β-ol and 14α-methyl-9β,19-cyclo-5α-ergost -25-en-3β-ol is reported for the first time in living organisms. The presence of 25-methylene sterols suggests that they, and not 24-methylene derivatives, are intermediates in the biosynthesis of sterols in C. sorokiniana.