Cellular Components Specifically Labeled during Sorbose Stimulation of Sugar Transport in Neurospora

Abstract

A number of independent systems for sugar transport in Neurospora have been postulated. An approach to identification of specific components of the sorbose transport system in ungerminated conidia pretreated with sorbose is described here. The fact that sorbose stimulates sorbose-uptake without causing germination was exploited in differential labeling experiments. Sorbose treated and untreated conidia were incubated with (3H) -leucine and (14C) -leucine respectively, and then mixed extracts fractionated on CM-cellulose at pH 4.75. Changes in the 3H/14C-ratio indicated sorbose-induced or -repressed substances. In selecting labeling conditions, care was taken to avoid errors that might arise from any differences in the internal amino acid pool size. The investigation revealed a buffer-soluble component repressed by sorbose and a Triton-soluble component induced by sorbose. The buffer-soluble, sorbose repressible protein is discussed in connection with the phenomenon of sorbose toxicity in Neurospora. The Triton-soluble, sorbose stimulated component, probably of carotenoid nature, is considered as a possible constituent of the sorbose transport system investigated here.