ISSN:0749-503X    

DOI:10.1002/yea.320070802

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractLactic acid‐grown cells of a strain ofKluyveromyces marxianustransportedD‐andL‐lactic acid by a saturable mechanism that was partially inducible and subject to glucose repression, with the following kinetic parameters at pH 5·4:Vmax= 1·00 (±0·13) mmol h−1per g dry weight andKs= 0·42 (±0·08) mM. Lactic acid transport was competitively inhibited by pyruvic, glycolic, acetic and bromoacetic acids. The latter, a non‐metabolizable analogue, was transiently accumulated, the extent depending on the extracellular pH. The pH dependence of theKsvalues for undissociated lactic acid and for the lactate anion indicated that the latter was the transported species. Lactate uptake was not accompanied by the simulatate uptake of protons, potassium ions or sodium ions excluding symport mechanisms. Initial lactic acid uptake led to transient membrane hyperpolarization as measured with a fluorescent dye excluding also an electroneutral anion antiport mechanism. It was concluded that lactate anions use a monocarboxylate uniport and that the counter anion, possibly bicarbonate, uses a separate channel, the coupling being elec

ISSN:0749-503X    

DOI:10.1002/yea.320070803

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractGenes encoding enzymes in the threonin/methionine biosynthetic pathwa were cloned and used to investigate their transcriptional response to signals known to affect gene expression on the basis of enzyme specific‐activities. Four major responses were evident: strong repression by methionine ofMET3,MET5andMET14, as previously described forMET3,MET2andMET25; weak repression by methionine ofMET6; weak stimulation by methionine but no response to threonine was seen forTHR1,HOM2andHOM3; no response to any of the signals tested, forHOM6andMES1. In aBOR3mutant,THR1,HOM2andHOM3mRNA levels were increased slightly. The stimulation of transcription by methionine forHOM2,HOM3andTHR1is mediated by theGCN4gene product and hence these genes are under the general amino acid control. In addition to the strong repression by methionine,MET5is also regulated by the general contro

ISSN:0749-503X    

DOI:10.1002/yea.320070804

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe membrane‐bound and soluble pyrophosphatase (PPase) activities ofSaccharomyces carlsbergenisvacuoles are determined by the functioning of special enzymes and are not due to non‐specific PPihydrolysis by other vacuolar phosphohydrolases. The molecular mass of the membrane‐bound PPase is apparently 120 000 and its molecule consists of three subunits with Mr= 41 000. Soluble PPase has a molecular mass of about 82 000 and includes three subunits with Mr= 28 000. Both enzymes are glycoproteins. The vacuolar membrane‐bound PPase is a prot

ISSN:0749-503X    

DOI:10.1002/yea.320070805

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have studied selective inactivation of alcohol oxidase (AO) in two peroxisome‐deficient (PER) mutants of the yeastHansenula polymorpha. In these mutants high activities of cytosolic AO are induced by different growth conditions. At enhanced expression rates AO is arranged in large crystalloids in the cytosol, whereas smaller crystalloids are often observed inside the nucleus. Transfer of cells of the PER mutant 125‐2E, which completely lacks peroxisomes, to glucose‐excess conditions did not lead to degradative inactivation of AO and catalase as observed in wild‐type (WT) cells used as a control. The gradual decrease in enzyme activities in the PER mutant could be accounted for by dilution of existing enzyme into newly formed cells as a result of growth. Morphologically, degradation of the cytosolic crystalloids was also not observed. Similar results were obtained with a second PER mutant (strain 124‐2D), impaired in the import of peroxisomal matrix proteins. This mutant is characterized by the presence of small peroxisomes and large cytosolic AO crystalloids. Upon a shift of cells to glucose‐excess conditions only part of the small peroxisomes present in these cells were degraded by mechanisms similar to those observed in WT cells placed under identical conditions. These results indicate that degradative inactivation of AO inH. polymorphais strictly dependent on the localization of the enzyme inside peroxisomes and furthermore suggests that the mechanisms triggering this process are not directed against AO protein, but instead, to the membrane surrounding the organelle. Transfer of cells to methanolor ethanol‐containing media both resulted in modification inactivation of AO. Under these conditions also the AO crystalloids remained unaffected by incubation in the ne

ISSN:0749-503X    

DOI:10.1002/yea.320070806

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractSaccharomyces cerevisiaecells treated by high voltage and made transformation‐competent (electroporation) are also made hyper‐recombinational as determined by an assay that measures interchromosomal mitotic recombination between chromosome III homologs, each containing mutant heteroallelic copies of thetrp1andhis3genes. There is a 10‐fold stimulation of Trp+and 21‐fold stimulation of His+prototrophs. Although this stimulation coincides with conditions for maximal transformation competence it is independent of the presence of transforming plasmid DNA. Electroporation does not increase the reversion frequency of these mutations, nor is there a stimulation in Ty transposition. Among the electroporation‐stimulated Trp+and His+recombinants there is no dramatic difference in the pattern of events: that is to say that, while there is an increase in the number of recombinants, the distribution of gene conversion and cross–over events among the stimulated recombinants is not significantly altered compared to spontaneously arising Trp+and His+recombinants. This electroporation‐stimulated recombination is abolished in an isogenicrad52mutant strain consistent with the increase in Trp+and His+prototrophs being the result of a stimulation of aRAD52‐dependent recomb

ISSN:0749-503X    

DOI:10.1002/yea.320070807

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractExoglucanases secreted by two different strains fromCandida albicanshave been purified to homogeneity. The purified enzyme from each strain behaved as a non‐glycosylated monomer (molecular weight 38 000) that was identical in terms of sodium dodecyl sulphate/polyacrylamide gel electrophoresis comigratin, amino acid analysis and amino terminal sequence. The amino acid composition was similar to that of the major exoglucanase fromSaccharomyces cerevisiae. In addition, these two enzymes displayed a 50% homology in the first 35 amino acids of the amino terminus. Antibodies against the deglycosylated exoglucanase (treated with Endo H) fromS. cerevisiaewere reactive with the exoglucanase fromC. albicansandvice versa. Immunoblotting proved to be a semiquantitative method to detectC. albicansantigen in culture fluids. The exoglucanase fromC. albicansappears to enter the secretory pathway without undergoing N‐glycosylat

ISSN:0749-503X    

DOI:10.1002/yea.320070808

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractRegulation of the two enzymes in reversetrans‐sulfuration was investigated inSaccharomyces cerevisiae. In wild‐type strains, cystathionine γ‐lyase, but not cystathionine β‐synthase, was derepressed nearly 15‐fold if cells were starved for both inorganic and organic sulfur compounds. In amet17strain which is defective of O‐acetylserine and O‐acetylhomoserine sulfhydrylase, the same enzyme was derepressed if organic sulfur compounds were limited; the repressive effect was in the order of glutathione>methionine>cysteine. The repressive effect of methionine was not observed, however, in acys2 cys4strain which is deficient of serine O‐acetyltransferase and cystathionine β‐synthase, indicating that methionine itself is not the effector. The weak repressive effect of cysteine was attributed to inefficient uptake of this amino acid.Our observations indicate that cystathionine γ‐lyase is the target of regulation in reversetrans‐sulfuration and that cysteine is very likely to be the ef

ISSN:0749-503X    

DOI:10.1002/yea.320070809

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractAlthoughSaccharomyces cerevisiaestrains had different cysteine uptake activities, they revealed monophasic uptake kinetics and had the sameKT(83·3 μM). The optimal pH of cysteine uptake was between 4·5 and 5·0, but the activity was quickly lost if cells were kept in buffer. When the activity was measured in the growth medium, it increased in the presence of EDTA and greatly decreased in the presence of mercuric chloride. Thioglycol as well as metabolic inhibitors such as dinitropherol and azide were inhibitory. Homocysteine and methionine were competitive and non‐competitive inhibitors, respectively. Cysteamine and cysteic acid were not inhibitory. From these observations, we conclude that the system mediating uptake of cysteine is specific (we thus name it the cysteine transport system) and that the cysteine transport system recognizes not only the SH‐group but also amino‐ and carboxyl‐groups.In wild‐type strains the cysteine transport system was derepressed only when the cells were incubated without any sulfur source. On the other hand, in cysteine‐dependent mutants, cysteine uptake activity increased with increase of exogenous supply of cysteine, glutathione or methionine. From this result, we suspect that the cellular cysteine level is the limiting factor for biosynthesis of the cysteine transport system in cysteine‐

ISSN:0749-503X    

DOI:10.1002/yea.320070810

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

ISSN:0749-503X    

DOI:10.1002/yea.320070811

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY