The Effect of n-polymethylene-carboxymaleimides on Glycine Movement into Pea Leaf Mitochondria

Abstract

Glycine decarboxylase is a multi-enzyme complex which is located on the inner surface of the inner mitochondrial membrane and catalyses the decarboxylation of glycine to serine (Moore et al., 1977; Sarojini, Oliver, 1983). Considerable controversy still exists as to whether glycine movement into the mitochondria occurs by simple diffusion (Day, Wiskich, 1980; Proudlove, Moore, 1982) or is carrier-mediated (Cavalieri, Huang, 1980; Walker et al., 1982). The latter suggestion is based upon the observations that glycine oxidation and glycine dependent swelling are inhibited by sulphydryl reagents. Direct uptake studies (Day, Wiskich, 1980; Proudlove, Moore, 1982) tended to suggest that glycine enters by simple diffusion, the effect of sulphydryl reagents being probably due to enzyme inhibition. In an attempt to discriminate between these two models we have investigated the effect of a series of N-polymethylenecarboxymaleimides (trivial name, acid maleimides-AM, see Figure 1) on glycine oxidation, decarboxylation and uptake by isolated pea leaf mitochondria. These compounds are a new class of membrane impermeant sulphydryl reagent (Griffiths et el., 1981) that can be used to determine the distribution of the sulphydryl groups in the hydrophobic regions of the membrane.