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E Schweizer

Publications and source records attributed to E Schweizer.

At least 163 records · Page 9Linked to original sources
PubMed1980

Fatty acid-requiring mutant of Saccharomyces cerevisiae defective in acetyl-CoA carboxylase.

The isolation and biochemical properties of a Saccharomyces cerevisiae mutant (acc1-167) defective in acetyl-CoA carboxylase [acetyl-CoA:carbon-dioxide ligase (ADP forming), EC 6.4.1.2] activity are described. The mutant is deficient in de novo biosynthesis of long-chain fatty acids and specifically requires a saturated fatty acid of chain length 14-16 C atoms for growth. Fatty acid synthetase levels were normal, but the acetyl-CoA carboxylase specific activity of the purified enzyme was reduced to approximately 5% compared to wild-type yeast. Upon sodium dodecyl sulfate/polyacrylamide gel electrophoresis the purified mutant enzyme migrated as a single band and was essentially indistinguishable from the wild-type enzyme. The study of acetyl-CoA carboxylase partial activities revealed that the biotin incorporation capacity and the transcarboxylase partial activity were unaffected whereas the biotin carboxylase component enzyme exhibited less than 10% of wild-type specific activity. This biotin carboxylase mutational deficiency could be ascribed to a more than 90% reduction of Vmax and to a comparable increase in the Km value for ATP, which was accompanied by an increased requirement for Mg2+. It is concluded that acc1-167 contains a structural gene mutation in the biotin carboxylase domain of acetyl-CoA carboxylase.

Acetyl-CoA Carboxylase↗
PubMed1980

Yeast mutants defective in acetyl-coenzyme A carboxylase and biotin: apocarboxylase ligase.

Among more than 7000 mutants of Saccharomyces cerevisiae, requiring saturated fatty acids, 61 acetyl-CoA-carboxylase-deficient strains have been identified. According to their mutual complementation characteristics these mutants have been assigned to two different genes, acc1 and acc2. Both acetyl-CoA carboxylase genes are unlinked to each other and to the fatty acids synthetase genes fas1 and fas2. The acetyl-CoA carboxylases of several acc1 and acc2 mutants have been purified and assayed for their overall and component enzyme activities. Besides overall acetyl-CoA carboxylation, which was lost in all cases, both component enzymes, biotin carboxylase and transcarboxylase, were simultaneously affected in most mutants, though often to a different relative extent. Similarly, the comparison of biochemical and genetic complementation data revealed no basis for a clear distinction between specific biotin carboxylase and transcarboxylase mutants. These results suggest that acc1 is a cluster gene coding for a multifunctional protein harboring both acetyl-CoA carboxylase component enzyme activities on the same polypeptide chain. The acetyl-CoA carboxylase isolated from acc2 mutants was free of biotin. Correspondingly, biotin:apoacetyl-CoA-carboxylase ligase activity was missing in acc2 mutants. Therefore, it is concluced that the primary defect in acc2 mutants is in the biotin:apocarboxylase ligase. In agreement with this conclusion, the acc2 acetyl-CoA carboxylase can be activated, in the presence of biotin and ATP, by ligase preparations from wild-type or acc1 mutant cells. By the use of these mutants, evidence was obtained that in vivo the biotinylation of both acetyl-CoA carboxylase and pyruvate carboxylase is catalyzed by the same ligase.

Acetyl-CoA Carboxylase↗
PubMed1978

Fatty acid biosynthesis in yeast.

Fatty acid synthetase and acetyl CoA carboxylase mutants have been used to study several aspects of fatty acid biosynthesis in yeast: the contribution of the various enzymes of fatty acid biosynthesis and modification to the overall cellular fatty acid composition, the mechanism of fatty acyl chain elongation in yeast, the molecular structure and the reaction mechanism of the fatty acid synthetase complex and the genetic control of the biosynthesis of this multi-enzyme system. Genetic and biochemical evidence suggest an alpha6beta6 molecular structure of this complex, where alpha and beta are multifunctional proteins comprising, respectively, 3 and 5 of the various fatty acid synthetase component functions. The two subunits alpha and beta are synthesized on two different, unliked genes, fas 2 and fas 1. The biosynthesis of both is coordinated. The various component enzyme activities reside in distinct domains on the multifunctional chains. While most domains appear to be functionally independent, the three acyl transferases exhibit extensive mutual interactions. It is suggested that the biosynthesis of a multifunctional protein is favoured on the grounds of kinetics and regulation as compared with the formation of a complex of the corresponding individual enzymes.

Acetyl-CoA Carboxylase↗
PubMed1977

[Biosynthesis and structure of the yeast fatty acid synthetase complex].

Genetic as well as biochemical data suggest that the yeast fatty-acid synthetase complex has an (AB)6 protein structure where A and B represent multifunctional polypeptide chains with molecular weights of 185000 and 180000 daltons, respectively. Subunit A contains at least 3 and subunit B4 of the 8 known biochemical functions of the multienzyme complex. It is concluded that this complex structure has evolved from the corresponding prokaryotic system of monofunctional enzymes due to a selective advantage regarding the biosynthesis and assembly of the complex components.

Fatty Acid Synthases↗
PubMed1976

End group analysis of yeast fatty acid synthetase.

The purified yeast fatty acid synthetase complex has been subjected to amino and carboxyl terminal amino acid end group analysis. Amino end groups were studied by Edman degradation and by dansylation of the sodium dodecyl sulfate- or urea-denatured complex. No N-terminal amino acid could be identified by either method. C-terminal amino acids were investigated by tritium labeling and by digestion of the complex with carboxypeptidases A and B. By both methods, the two amino acids valine and lysine were consistently identified as the C-termini of two different polypeptide chains. After separation of the fatty acid synthetase subunits A and B by sodium dodecyl sulfate polyacrylamide gel electrophoresis lysine was identified as the C-terminus of subunit A and valine as that of subunit B. The results are interpreted as evidence that the yeast fatty acid synthetase complex is basically composed of two nonidentical and multifunctional polypeptide chains.

Amino Acid Sequence↗
PubMed1976

Control of fatty-acid synthetase levels by exogeneous long-chain fatty acids in the yeasts Candida lipolytica and Saccharomyces cerevisiae.

Endogeneous fatty acid biosynthesis in the two yeast species, Saccharomyces cerevisiae and Candida lipolytica is completely repressed by the addition of long-chain fatty acids to the growth medium. In Candida lipolytica, this repression is accompanied by a corresponding loss of fatty acid synthetase activity in the cell homogenate, when the cells were grown on fatty acids as the sole carbon source. The activity of the Saccharomyces cerevisiae fatty acid synthetase, however, remains unaffected by the addition of fatty acids to a glucose-containing growth medium. From fatty-acid-grown Candida lipolytica cells no fatty acid synthetase complex can be isolated, nor is there any immunologically cross-reacting fatty acid synthetase protein detectable in the crude cell extract. From this it is concluded that Candida lipolytica, but not Saccharomyces cerevisiae, is able to adapt to the growth on fatty acids either by repression of fatty acid synthetase biosynthesis or by a fatty-acid-induced proteolytic degradation of the multienzyme complex. Similarly, the fatty acid synthetase complex disappears rapidly from stationary phase Candida lipolytica cells even after growth in fatty-acid-free medium. Finally, it was found that the fatty acid synthetase complexes from Saccharomyces cerevisiae and Candida lipolytica, though very similar in size and subunit composition, were immunologically different and had no common antigenic determinants.

Acetyl-CoA Carboxylase↗
PubMed1975

Temperature-sensitive mutants of the yeast fatty-acid-synthetase complex.

By genetic complementation analysis, 88 independently isolated temperature-sensitive fatty acid synthetase mutants have been assigned to the six different fas-complementation groups II (fas 1), III (fas 1), Vb (fas 1), VI (fas 2), VIII (fas 2) and IX (fas 2). The complementation groups Va, Vc, Vd, IV and VII observed among nonconditional fas-mutants have not been found among the temperature-sensitive strains studied. From the failure to detect pantetheine-deficient conditional fas-mutants it is concluded that the yease acyl-carrier protein has an exceptionally stable tertiary structure. Furthermore, the lack of temperature-sensitive mutants of complementation group IV possibly indicates that this group specifically represents only nonsense and frameshift mutations. Almost half of the temperature-sensitive fas 1 and fas 2 mutants studied exhigited non-complementing characteristics. These results confirm the existence of non-complementing fas1 and fas2 missense mutations. From this it is concluded that both fatty acid synthetase loci encode multifunctional polypeptide chains rather than several monofunctional component enzymes. The possible existence of an independent acyl-carrier protein, as suggested by the genetic data reported in this study, is discussed. With 10 different temperature-sensitive fas1 and fas2 mutants the dependence of cellular growth rates on growth temperature and fatty acid supplementation was determined. With all mutants studied fatty-acid-independent growth was completely suppressed at non-permissive temperatures (34 -37 degrees C). In fatty-acid-supplemented media, however, these mutants exhibited the same growth characteristics as wild-type yeast cells. In contrast to this, wild-type yeast growth was found to be fatty-acid-independent at all temperatures studied. Other than in vivo, the purified fatty acid synthetase isolated from five different temperature-sensitive fas1 and fas2 mutants exhibited in vitro no increased thermolability compared to the wild-type enzyme. From this it is concluded that the specific conformation of fatty acid synthetase subunits either forms only at the ribosomal level during translation, or that this conformation is stabilized by the assembly of subunits into the multienzyme complex structure.

Binding Sites↗
PubMed1975

Control of fatty-acid synthetase biosynthesis in Saccharomyces cerevisiae.

143 out of 308 fas1 mutants (47%) and 139 out of 443 fas2-mutants (32%) genetically studied in this laboratory fail to complement with any other fas-mutant (deficient in fatty acid synthetase) of the same gene locus. From these noncomplementing fas-mutants no mutant fatty acid synthetase can be isolated using the wild-type enzyme purification procedure. Furthermore the noncomplementing fas-mutants generally contain no material immunologically crossreacting with a specific fatty acid synthetase antiserum. However, subunits obtained after dissociation of the complex with sodium dodecylsulfate still cross react with this antiserum. Therefore, it is concluded that noncomplementing fas-mutants contain no fatty acid synthetase component proteins, though one of the two fas-loci is mutationally unaffected. This conclusion was further confirmed by 14C-labeled amino acid incorporation studies which indicated that in noncomplementing fas-mutants, other than in wild type and complementing fas-mutant cells, no label was incorporated into fatty acid synthetase subunits or precursor proteins. At nonpermissive temperature, the same biochemical and immunological characteristics were observed with temperature-sensitive non-complementing fas-mutants. These results suggest that noncomplementing fas-mutants either represent regulatory mutants unable to induce the mutationally unaffected other fas-gene locus or that they are association-defective mutants. In both cases the resulting individual subunits of the complex may be rapidly degraded by intracellular proteases.

Fatty Acid Synthases↗
PubMed1975

Malonyl and palmityl transferase-less mutants of the yeast fatty-acid-synthetase complex.

146 independently isolated mutants of the fatty acid synthetase gene locus fas 1 were subdivided into six different complementation groups. Three of these groups, Va, Vb and Vd, have not been described before. The mutant fatty acid synthetases isolated from representatives of complementation group Vb were specifically deficient in two component enzymes at the same time, the malonyl and palmityl transferases. Among more than 180 fas 1 and fas 2 mutants systematically screened for malonyl and palmityl transferase activities no mutant was found affected in only one of these two fatty acid synthetase component enzymes. From this it is concluded that both transfer reactions are catalyzed by the same enzyme. In any malonyl transferase-less fatty acid synthetase, neither of the two known malonyl binding sites, i.e. enzyme-bound pantetheine and the non-thiol binding site, accepts malonate. This indicates that malonate is transferred to both groups by the same enzyme. So far, no acetyl transferase-less fas mutants have been characterized. On the other hand, the mutants of two fas 1 complementation groups, Va and Vd, though negative in overall fatty acid synthetase activity had no deficiency in any of the known component enzymes which can be tested in vitro. A possible interrelationship between both findings is discussed.

Acyltransferases↗
PubMed1975

Studies on magnesium's mechanism of action in digitalis-induced arrhythmias.

The mechanism by which magnesium affects digitalis-induced arrhythmias was studied in dogs with and without beta-receptor blockade. Digoxin was infused at a rate of 2.5mug/kg/min until ventricular tachycardia developed, then half the animals were given MgSO4, the other half saline. In animals given MgSO4, sinus rhythm was immediately re-established; in animals given saline, ventricular tachycardia persisted. In animals with beta-receptor blockade, MgSO4 was as effective in abolishing ventricular tachycardia as in those without beta-receptor blockade. We found no evidence that magnesium re-activated digoxin-inhibited (Na+, K+)-ATPase, altered myocardial or microsomal digoxin binding, or acted via the autonomic nervous system. Magnesium's direct effect on calcium and potassium fluxes across the myocardial cell membrane may be the mechanism of its antiarrhythmic action in digitalis-toxic arrhythmias.

Animals↗
PubMed1974

Saturated fatty acid mutant of Saccharomyces cerevisiae with an intact fatty acid synthetase.

A Saccharomyces cerevisiae conditional mutant, LK 181, is described which grows at 37 C only when supplemented with a saturated fatty acid of 12 to 14 carbon atoms chain length. At 22 C, however, no fatty acid supplementation is required for growth. The fatty acid concentration required for optimal growth at 37 C is about four times lower for LK 181 than for fatty acid synthetase-deficient mutants. In contrast to all fatty acid synthetase mutants so far examined, mutant LK 181 cannot grow with palmitic acid. The addition of palmitic, palmitoleic, or oleic acid to the culture medium prevents LK 181 growth at temperatures between 22 and 37 C. In vivo as well as in vitro, cellular de novo fatty acid biosynthesis from acetate is unimpaired in this mutant. It is suggested that endogenously synthesized fatty acids, due to their chain lengths of 16 and more carbon atoms, cannot supplement the mutant LK 181. It is concluded that the exogeneously supplied fatty acids act as allosteric effectors for a mutationally altered cellular protein to restore its biological function at elevated temperatures, rather than as a substitute for endogenously synthesized long-chain fatty acids.

Acetates↗