S-Adenosylhomocysteine hydrolase deficiency in cysteine auxotrophs of Tetrahymena thermophila.
The biochemical lesion in two cysteine auxotrophs of Tetrahymena thermophila has been established as a defect in S-adenosylhomocysteine hydrolase, an enzyme of the transsulfuration pathway. As a result, these mutants require cysteine (or cystathionine or homocysteine) for growth in a defined medium. Cell-free extracts of the mutants contained less than 5% of the level of the enzyme seen in the wild type. One of the mutant strains accumulated intracellular levels of S-adenosylhomocysteine as high as 1380 microM, a level 200 times normal. When both mutant strains were maintained in defined medium without cysteine, growth occurred after a long lag; this phenomenon was termed "adaptation." Adaptation was a) reversed by passage through rich medium, b) was not a recovery of S-adenosylhomocysteine hydrolase, and c) was probably linked to induction of an alternate pathway for cysteine biosynthesis, involving a lysosomal S-adenosylhomocysteine nucleosidase activity.
D043383:Adenosylhomocysteinase; D000818:Animals; D019757:Carbon-Oxygen Lyases; D003470:Culture Media; D003545:Cysteine / Q000096:biosynthesis* / Q000494:pharmacology; D006867:Hydrolases / Q000378:metabolism*; D008190:Lyases / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D009154:Mutation; D009699:N-Glycosyl Hydrolases / Q000378:metabolism; D012435:S-Adenosylhomocysteine / Q000378:metabolism; D013768:Tetrahymena / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development
D003470:Culture Media; D012435:S-Adenosylhomocysteine; D008715:Methionine; D006867:Hydrolases; D009699:N-Glycosyl Hydrolases; C019606:adenosylhomocysteine nucleosidase; D043383:Adenosylhomocysteinase; D008190:Lyases; D019757:Carbon-Oxygen Lyases; C045411:serine sulfhydrolyase; D003545:Cysteine