Apparent transinhibition of peptide uptake in the scutellum of barley grain

The uptake of glycylsarcosine (Gly‐Sar) into scutella separated from germinating grains of barley (Hordeum vulgare L. cv. Himalaya) is inhibited by other peptides; in most cases the inhibition is not purely competitive but of a mixed type (simultaneous increase in the apparent Km and decrease in Vmax) (Sopanen, T. 1979. FEBS Lett. 108: 447–450). The aim of the present experiments was to elucidate the mechanism of the mixed inhibition by studying how peptides already taken up into the cells affect the uptake of Gly‐Sar. When scutella were preincubated in the presence of various peptides, 11 of the 13 peptides tested inhibited the subsequent uptake of Gly‐Sar by 10 to 45%. The inhibition, stu…