The cleavage and synthesis of cystathionine in wild type and mutant strains of Neurospora crassa

Wild type Neurospora was found to cleave cystathionine to cysteine and to homocysteine. A mutant which requires homocysteine for growth was found to have no enzyme for the production of homocysteine from cystathionine. A cystathionine-requiring mutant was foound to be deficient in the cysteine-producing enzyme. It was found that a suppressor, obtained by Giles, which causes these mutants to grow on minimal medium, returns enzyme activity to the mutants. A paper chromatographic method for the determination of cystathionine is described. Evidence is presented that transsulfuration in Neurospora is a reversible process.