The essentiality of sulfhydryl groups to transport in Neurospora crassa

Three active transport systems for amino acids and another for glucose in germinated conidia of Neurospora were all inactivated during incubation with the sulfhydryl reagents N-ethylmaleimide, p-chloromercuribenzoate, and iodoacetamide. Where tested, the inactivation by p-chloromercuribenzoate was reversed by the action of dithiothreitol. However, two other sulfhydryl reagents, the chloromethyl ketone derivatives of leucine and lysine, were found to have differential effects on the various transport systems. Inactivation by these two compounds did not occur at the active site of the permeases by affinity labeling, suggesting differential availability of sulfhydryl groups among the transport systems. Also, inactivation by these reagents was greatly enhanced in the presence of p-chloromercuribenzoate.