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A Paszewski

Publications and source records attributed to A Paszewski.

At least 37 records · Page 2Linked to original sources
PubMed1992

Biosynthesis of sulphur amino acids in Saccharomyces cerevisiae: regulatory roles of methionine and S-adenosylmethionine reassessed.

cys4-1, a mutation in the reverse trans-sulphuration pathway, relieves the sulphate assimilation pathway and homocysteine synthase from methionine-mediated repression. Since the mutation blocks the synthesis of cysteine from methionine downstream from homocysteine, this indicates that neither methionine nor S-adenosylmethionine serve as low-molecular-mass effectors in this regulatory system, contradicting earlier hypotheses.

Amino Acids, Sulfur↗
PubMed1990

A yeast with unusual sulphur amino acid metabolism.

A yeast strain highly resistant to propargylglycine (an inhibitor of cystathionine gamma-lyase) was isolated from air. It was partially characterized, but it has not been identified with any known yeast species. Its sulphur amino acid metabolism differed from that of other fungi by the lack of the reverse transsulphuration pathway from methionine to cysteine, as no activity of cystathionine beta-synthase or cystathionine gamma-lyase was found. The functional lack of this pathway was confirmed by growth tests and by experiments with [35S]methionine. In contrast to Saccharomyces cerevisiae neither homocysteine synthase nor the sulphate assimilation pathway were repressible by methionine in the new strain; on the contrary, a regulatory effect of cysteine was observed.

Alkynes↗
PubMed1989

Interrelated regulation of sulphur-containing amino-acid biosynthetic enzymes and folate-metabolizing enzymes in Aspergillus nidulans.

In Aspergillus nidulans homocysteine can be metabolized both to cysteine and methionine. Mutants impaired in the main pathway of cysteine synthesis or in the sulphate assimilation pathway show a low pool of glutathione and elevated levels of homocysteine synthase and of the homocysteine-to-cysteine pathway enzymes. On the other hand, the level of methionine synthase and other enzymes of folate metabolism is depressed in these mutants. This anticoordinated regulation provides a mechanism controlling the partition of homocysteine between the two diverging pathways. Homocysteine synthase was found derepressed, along with folate enzymes, in a strain carrying a mutation which suppresses mutations in metA, metB and metG genes. These results indicate that homocysteine synthase can be regarded as the enzyme of an alternative pathway of methionine synthesis and strongly suggest that the regulatory mechanisms governing sulphur-containing amino acid and folate metabolisms are interrelated.

Amino Acids↗
PubMed1988

Sulphate and methionine as sulphur sources for cysteine and cephalosporin C synthesis in Cephalosporium acremonium.

Three prototrophic strains of Cephalosporium acremonium with different potentials for cephalosporin C production show pronounced differences in pools of intracellular sulphur amino acids. The superior strain exhibits the largest pool, particularly of cysteine (four times that of the non-producing strain). In fermentations with this strain methionine was found to be a much better sulphur source than sulphate for both cysteine and antibiotic synthesis. In the presence of methionine the utilization of sulphate is strongly depressed.

Acremonium↗
PubMed1987

Regulation of sulphur amino acids metabolic enzymes in Cephalosporium acremonium strains differing in antibiotic production.

Three strains of Cephalosporium acremonium with different potential of cephalosporin C production show differences in the levels of sulphur amino acid metabolic enzymes. The regulation of these enzymes is also different in the strains. In the superior producing strain two enzymes directly involved in cysteine synthesis are the least susceptible to repression by methionine. In this strain cystathionine metabolizing enzymes seem to favour cysteine synthesis. Antibiotic producing strains, in contrast to the non-producing strain, are highly sensitive to chromate.

Acremonium↗
PubMed1984

Mutations affecting the sulphur assimilation pathway in Aspergillus nidulans: their effect on sulphur amino acid metabolism.

Several sul-reg mutants of Aspergillus nidulans isolated as constitutive for arylsulphatase were studied with respect to the regulation of enzymes involved in cysteine and homocysteine synthesis and to the pool of sulphur amino acids. All mutants examined showed a decreased concentration of glutathione as compared with the wild type, and all mutants, with one exception, had a decreased total pool of sulphur amino acids. The results suggest that the mutants are leaky in the sulphate assimilation pathway. They show derepression of cysteine synthase, homocysteine synthase, cystathionine beta-synthase and gamma-cystathionase. In spite of having derepressed homocysteine synthase, the enzyme which constitutes an alternative pathway for homocysteine synthesis, the sul-reg mutations do not suppress lesions in genes required for the main homocysteine-synthesizing pathway. This indicates that the derepression of homocysteine synthase is not in itself sufficient for physiological functioning of this enzyme, but seems to depend also on the effectiveness of cysteine synthesis and sulphide formation.

Amino Acids, Sulfur↗
PubMed1982

Metabolism of 5'-methylthioadenosine in Aspergillus nidulans. An alternative pathway for methionine synthesis via utilization of the nucleoside methylthio group.

Experiments in which 5'-methylthioadenosine was used as a culture supplement for methionine-requiring mutants of Aspergillus nidulans with various enzymatic lesions indicated that the methylthio group derived from the nucleoside can be recycled to methionine. The results strongly suggest that methionine may be synthesized in the reaction catalyzed by homocysteine synthase (EC 4.2.99.10) in which O-acetylhomoserine is an acceptor of the methylthio group. The first step on the salvage pathway of the methylthio group is, in Aspergillus nidulans, phosphorolytic cleavage of 5'-methylthioadenosine to adenine and 5-methylthioribose 1-phosphate catalyzed by a specific phosphorylase.

Adenosine↗
PubMed1982

Cysteine and homocysteine synthesis in Saccharomycopsis lipolytica; identification and characterization of two cysteine synthases.

In Saccharomycopsis (Candida) lipolytica direct cysteine synthesis is mediated by two different, simultaneously acting cysteine synthases: a low molecular mass (74,000 daltons) monofunctional enzyme (Km for O-acetyl-l-serine 23.5 mm) and a high molecular mass (220,000 daltons) bifunctional cysteine-homocysteine synthase (Km for O-acetyl-l-serine 55.0 mm). The latter enzyme is also involved in direct homocysteine synthesis from O-acetyl-l-homoserine (Km 11.9 mm). Evidence is presented that a fraction of homocysteine can be synthesized from cysteine via cystathionine. Our previous results (Morzycka & Paszewski, FEBS Lett., 1979, 101, 97-100; Mol. Gen. Genet., 1979, 174, 33-38) together with the data presented here strongly suggest that both S., lipolytica synthases are under control of the same regulatory system, together with the other enzymes of sulphur metabolism: ATP-sulphurylase and aryl-sulphatase. gamma-Cystathionase, an enzyme involved in cysteine synthesis from homocysteine, is controlled exclusively by cysteine.

Ascomycota↗
PubMed1981

The cell-free protein synthesis system from the 'slime' mutant of Neurospora crassa. Preparation and characterisation of importance of 7-methylguanosine for translation of viral and cellular mRNAs.

A simple procedure for preparation of a cell-free protein synthesis system (23000 X g supernatant) from the protoplast-like 'slime' mutant of Neurospora crassa is described. A variety of messenger RNAs of viral and cellular origin could be efficiently and faithfully translated in this system into proteins with Mr as large as 180000. The importance of the 7-methylguanosine cap for mRNA translation in the Neurospora system was studied in detail using the cap analogs and chemically decapped messengers. As in the case of reticulocyte lysate or wheat germ extract, the extent of m7G requirement for mRNA translation in a fungal extract strongly depended on translation conditions such as incubation temperature or concentration of potassium ions, mRNA and 23000 X g supernatant protein.

Animals↗
PubMed1980

Effect of regulatory mutations of sulphur metabolism on the levels of cysteine- and homocysteine-synthesizing enzymes in Neurospora crassa.

1. Regulation of four enzymes involved in cysteine and homocysteine synthesis, i.e. cysteine synthase (EC 4.2.99.8), homocysteine synthase (EC 4.1.99.10), cystathionine beta-synthase (EC 2.1.22) and gamma-cystathionase (EC 4.4.1.1) was studied in the wild type and sulphur regulatory mutants of Neurospora crassa. 2. Homocysteine synthase and cystathionine beta-synthase were found to be regulatory enzymes but only the former is under control of the cys-3 - scon system regulating several enzymes of sulphur metabolism, including gamma-cystathionase. 3. The results obtained with the mutants strongly suggest that homocysteine synthase plays a physiological role as an enzyme of the alternative pathway of methionine synthesis. Cysteine synthase activity was similar in all strains examined irrespective of growth conditions. 4. The sconc strain with derepressed enzymes of sulphur metabolism showed an increased pool of sulphur amino acids, except for methionine. Particularly characteristic for this pool is a high content of hypotaurine, a product of cysteine catabolism.

Carbon-Oxygen Lyases↗
PubMed1979

Regulation of s-amino acids biosynthesis in Saccharomycopsis lipolytica.

ATP-sulfurylase, cysteine synthase, homocysteine synthase, arylsulfatase and beta-cystathionase in Saccharomycopsis lipolytica are repressed on the addition of methionine, homocysteine or cysteine to the growth medium. The use of appropriate mutants enabled us to demonstrate that the synthesis of these enzymes is regulated by the system involving at least two low-molecular weight effectors--most likely cysteine and methionine (or their close derivatives).

Amino Acids, Sulfur↗