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Biomedical subjects

A Paszewski

Publications and source records attributed to A Paszewski.

At least 55 records · Page 3Linked to original sources
PubMed1976

Methionine overproduction by Saccharomycopsis lipolytica.

Six ethionine-resistant (Etr) regulatory mutants of Saccharomycopsis lipolytica Sl/1 overproducing methionine have been isolated. Five of them are also resistant to seleno-methionine. The activity of homocysteine synthase (O-acetyl-L-hormoserine-acetate lyase, adding hydrogen sulfide) is derepressed in these mutants and is not susceptible to the methionine-mediated repression. The pool of free methionine in Etr mutants is enhanced 1.5 to 18 times, and incorporation of 35S into methionine is 1.5 to 50 times higher than that in the wild strain. Neither accumulation of endogenous free methionine in Etr mutants nor the uptake of exogenous methionine is accompanied by an increase in the S-adenosylmethionine pool. This implies compartmentation of methionine metabolism in S. lipolytica.

Ascomycota↗
PubMed1976

On sulfhydrylation of O-acetylserine and O-acetylhomoserine in homocysteine synthesis in yeast.

Considerable differences in the activities of cysteine and homocysteine synthase (EC 4.2.99.8), and in the ratio of these activities were observed in yeast strains representing different genera and species. This suggests that homocysteine synthesis directly from O-acetylhomoserine may predominate in some strains, whereas in the others homocysteine is formed from cysteine via cystathionine.

Candida↗
PubMed1975

Enzymatic lesions in methionine mutants of Aspergillus nidulans: role and regulation of an alternative pathway for cysteine and methionine synthesis.

In Aspergillus nidulans the pathway involving cystathionine formation is the main one for homocysteine synthesis. Mutants lacking cystathionine gamma-synthase or beta-cystathionase are auxotrophs suppressible by: (i) mutations in the main pathway of cysteine synthesis (cysA1, cysB1, and cysC1), (ii) mutations causing stimulation of cysteine catabolism (su101), and (iii) mutations in a presumed regulatory gene (suAmeth). A relative shortage of cysteine in the first group of suppressors causes a derepression of homocysteine synthase, the enzyme involved in the alternative pathway of homocysteine synthesis. A similar derepression is observed in the suAmeth strain. Homocysteine synthesized by this pathway serves as precursor for cysteine and methionine synthesis. A mutant with altered homocysteine synthase is a prototroph, indicating that this enzyme is not essential for the fungus.

Aspergillus nidulans↗
PubMed1975

Homolanthionine in fungi: accumulation in the methionine-requiring mutants of Aspergillus nidulans.

Homolanthionine, a higher homologue of cystathionine, was found to accumulate in the mutants of Aspergillus nidulan impaired in the synthesis of methionine from homocysteine. The additional introduction of mutation resulting in a block at cystathionine gamma-synthase but not at cystathionine beta-synthase abolishes accumulation of both homolanthionine and cystathionine. This suggests a possible participation of cystathionine gamma-synthase in homolanthionine synthesis.

Aspergillus nidulans↗
PubMed1974

Dr Barbara Dudziak.

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History, 20th Century↗
PubMed1970

Chloroplast structure and function in ac-20, a mutant strain of Chlamydomonas reinhardi. II. Photosynthetic electron transport.

Photosynthetic electron transport is markedly affected in mixotrophic cells of ac-20 because they lack the capacity to form the wild-type level of cytochrome 559, as well as Q, the quencher of fluorescence of photochemical system II. The other components of the electron-transport chain, as well as reactions dependent upon photochemical system I, are unaffected in the mutant strain. These observations are discussed in terms of the previously reported effects of the ac-20 mutation on CO(2) fixation and ribulose-1,5-diphosphate carboxylase activity.

Chlorophyll↗