Observations on the effects of methionine and homocysteine on growth of a cholineless mutant of Neurospora crassa

Abstract

Homocysteine alone failed to support growth of Neurospora crassa mutant strain no. 34486. In the presence of suboptimum concentration of methionine, it stimulated growth up to a concentration of 75 ng/ml, beyond which inhibition was observed. These effects were independent of the presence of pteroylglutamic acid or the C1 donors formate and serine. Stimulation was not observed when choline was substituted for methionine. Homocysteine produced inhibition of growth of wild-type Neurospora crassa in the presence or absence of methionine or choline. Increase in concentrations of boron (as borate), molybdenum (as moiybdate), Fe2+, Cu2+, Mn2+ and Zn2+ ions in the medium eliminated inhibition partially in the cholineless mutant and completely in wild-type Neurospora crassa.