Inhibitor-dependent, reciprocal changes in the activities of glyceraldehyde 3-phosphate dehydrogenases in Sinapis alba cotyledons

Abstract

Summary Glyceraldehyde 3-phosphate dehydrogenases (GPD) from cotyledons of far-red- light-grown Sinapis alba seedlings can be separated by ammonium sulfate chromatography into two enzymes designated NAD-GPD I and NADP-GPD • NAD-GPD II. The former species is probably the NAD-GPD of cytoplasmic glycolysis (EC 1.2.1.12). The latter species has both NADP and NAD activity and is apparently identical to the NADP-GPD of plastids (EC 1.2.1.13). When puromycin (100 μg • ml-1) or D-threo chloramphenicol (200 μg • ml-1) is applied to seedlings, the light-dependent increase in the activities of the bifunctional enzyme is strongly inhibited. The resultant decrease in NAD-GPD II activity of this enzyme is accompanied by an equivalent increase in NAD-GPD I activity. The application of actinomycin D (10 μg • ml-1) affects neither of these two enzymes, but significantly inhibits the activity increase of the control enzyme glyoxylic acid reductase (EC 1.1.1.26). These and other regulatory data published previously are discussed on the basis of a model proposing that the formation of glyceraldehyde 3-phosphate dehydrogenases proceeds sequentially via an anabolic pathway in which the glycolytic enzyme of the cytoplasm functions as a precursor or subunit of the bifunctional chloroplast enzyme.