Sterol synergism as previously observed ) Biochemistry 19, 1462-1467 and defined as a greater-than-additive growth response to pairs of sterols by Mycoplasma capricolum [Dahl, J. S., Dahl, C. E. & Bloch, K. (1981) J. BioL Chem. 256, 87-91] is now demonstrated in the yeast mutant GL7, which is auxotrophic for sterol and unsaturated fatty acid. Mutant cells growing poorly when provided with cholesterol and oleic acid respond to ergosterol supplements (ergosterol-to-cholesterol ratio, 1:3) by a pronounced increase in growth rates and cell yields. Stigmasterol also elicits a significant synergistic effect, and 7-dehydrocholesterol, a smaller one. Evidence for a metabolic role of ergosterol in yeast membranes is presented. Cells raised on a 1:3 mixture of ergosterol to cholesterol up to midlogarithmic phase subsequently incorporate [1-'4C]oleic acid at significantly faster rates into phospholipids than do cells grown on cholesterol alone.In a series ofreports, we have described a phenomenon termed "sterol synergism" on the basis of the following observations. The sterol auxotroph Mycoplasma capricolum grows optimally on cholesterol but only poorly on lanosterol (1, 2). Bacterial cells supplied simultaneously with two sterols, cholesterol in limiting and lanosterol in nonlimiting quantities, grow much more rapidly and with higher yields than do cells receiving cholesterol or lanosterol alone (3). The response is synergistic, not additive. These findings were taken to indicate more than one function for sterols in membranes, and supporting evidence has been published (4). Here we describe a similar phenomenon for an eukaryotic cell, the yeast mutant GL7, chosen because it has an absolute sterol requirement for growth (5).In designing the present experiments, we took advantage of the facts that (i) GL7, a mutant deficient in both squalene epoxide cyclase and heme synthesis (5), grows optimally when supplied with ergosterol and one of a variety of mono-or polyunsaturated fatty acids, but (ii) cholesterol, a sterol foreign to yeast, replaces ergosterol effectively only when either linoleate or a mixture of palmitoleate and oleate serves as the external fatty acid source. When oleate is the only fatty acid supplied, growth on cholesterol is much slower than on ergosterol (6). We now find that under these latter conditions, ergosterol in amounts too small to elicit detectable growth by itself raises the growth rate of GL7 cells by a large factor.We also note that the sterol requirement for GL7 is remarkably small. Grown on a nearly optimal supply of ergosterol, these cells contain about 10% of the total sterol that wild-type yeast normally produces. Spheroplasts of GL7 cells grown on different sterol concentrations or "synergistic" sterol mixtures were fractionated, and subcellular membrane fractions were analyzed for their relative sterol and phospholipid content. Finally, we report that mutant cells raised on ergosterol/cholesterol show an enhanced capacity to incorporate external oleic acid into cellular phosph...

Chrysophanol and islandicin, two anthraquinones which are structurally related to emodin, were found to be frame-shift mutagens for Salmonella typhimurium strain TA 1537 after metabolic activation.

The relatively slow growth rate of the yeast mutant GL7, a sterol auxotroph, on medium containing cholesterol is markedly accelerated by supplementation with small amounts of ergosterol. Under these conditions (sterol synergism) cellular phospholipid synthesis is enhanced. We now find that one of the ergosterol-stimulated processes is the methylation of phosphatidylethanolamine to phosphatidylcholine. This is shown by comparing methyltransferase activities of membrane preparations derived from cells grown on either ergosterol, cholesterol, or the synergistic sterol pair. Incorporation of 32p from [y-32P]ATP into the yeast membranes is rapid and greater when ergosterol-grown cells rather than cholesterol-grown cells are the source of membranes.Under defined culture conditions, selected pairs of sterols promote substantially faster growth of the sterol auxotrophs Mycoplasma capricolum (1) and the yeast mutant GL7 (2) than do the corresponding sterols individually. We refer to this growth response, which is greater than additive, as sterol synergism. In M. capricolum a marked synergistic effect is seen with a 20:1 mixture of lanosterol and cholesterol, whereas for the yeast mutant a 3:1 mixture of cholesterol and ergosterol is the most effective pair. The optimal single sterol for supporting the growth of mycoplasma is cholesterol; for yeast it is ergosterol. In our view the synergistic growth responses we have observed with pairs of sterols are manifestations of dual or multiple functions of sterols in certain membrane systems (1-3). The conventional function, modulation of the membrane physical state, is assigned to the major component and distinguished from the role of the minor sterol component, which involves control of some metabolic membrane-associated processes. Evidence for such sterol-specific metabolic interventions in phospholipid biosynthesis has been reported. In M. capricolum cholesterol lowers the Km for oleic acid uptake and incorporation into phosphatidylglycerol severalfold (4). In the yeast mutant GL7, cellular ergosterol accelerates the rates of synthesis of all membrane phospholipids, as judged by incorporation of oleic acid (2).In exploratory experiments designed to identify ergosterolsensitive partial reactions of yeast phospholipid synthesis the first trial was negative. Fatty acyl-CoA synthetase activities in extracts of cells grown either on ergosterol or cholesterol were identical. Examining the transmethylation pathway for the synthesis of phosphatidylcholine (PtdCho) we observed, however, an ergosterol-specific promotion of enzyme activity. First, we found that yeast cells grown on ergosterol or ergosterol/cholesterol mixtures incorporate substantially more radioactivity from [methyl-3H]methionine into PtdCho and its partially methylated precursors than cells grown on cholesterol alone. This observation pointed to a role for the prototypic yeast sterol in the S-adenosylmethionine-mediated methylation of phosphatidylethanolamine (PtdEtn) to PtdCho. In accord with this expectatio...

Die toxischen Cyclopeptide Islanditoxin (I) und Cyclochlorotin (II) aus Penicillium Islandicum werden in ihrer Struktur sichergestellt.

Dedicated to Professor John C. Sheehan on the occasion of his sixty‐fifth birthday. The structures of cyclochlorotine and islanditoxin, cyclic peptides from Penicillium islandicum are reviewed. The peptide A isolated in these laboratories has been identified by gc/ms studies as cyclochlorotine. It is suggested that the structure of islanditoxin [cyclo‐(L‐dichloroprolyl‐D‐β‐amino‐β‐phenylpropionyl‐L‐α‐amino‐n‐butyryl‐L‐seryl‐L‐serine)] 1 should now be revised to that of cyclochlorotine, [cyclo‐(L‐dichloroprolyl‐D‐β‐amino‐n‐butyryl‐L‐seryl‐L‐β‐amino‐β‐phenyl‐propionyl‐L‐serine)] 2.