Several mutants of 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 β -synthase and γ-cystathionase. In spite of having derepressed homocysteine synthase, the enzyme which constitutes an alternative pathway for homocysteine synthesis, the 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.


Article metrics loading...

Loading full text...

Full text loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error