STUDY OF FOLIC ACID DERIVATIVES IN NEUROSPORA CRASSA AND THE RECOGNITION OF A MUTANT RESISTANT TO AMINOPTERIN

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Abstract
Folic acid derivatives accumulate in Neurospora crassa as one or more polyglutamyl conjugates. They appear to be present as hydrogenated forms of pteroylglutamic acid. Evidence also indicates that labile precursors or products of these hydrogenated forms exist which can be measured as citrovorum factor activity by heating with ascorbate. The folic acid derivatives are subject to breakdown by N. crassa and their concentration decreases with the age of the culture. N. crassa can also inactivate pteroylglutamic acid itself and the antagonist, aminopterin. It has been shown that neither choline nor N5-formyl tetrahydro pteroylglutamic acid will reverse aminopterin toxicity in wild-type N. crassa. A choline-requiring mutant has been shown to be highly resistant to aminopterin inhibition.