SUBUNIT STRUCTURE OF 3 GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASES OF SOME FLOWERING PLANTS

A procedure is described for the purification of three glyceraldehyde phosphate dehydrogenases from a batch of beet leaves. Glyceraldehyde 3-phosphate:NADP+ reductase, nonphosphorylating (EC 1.2.1.9) has been purified over 1500-fold. The Mr of this enzyme is 190,000 and its subunits have an Mr of 53,000, suggesting a tetramer as the active form. Its pI is 6.0. Cytosolic glyceraldehyde 3-phosphate dehydrogenase, NAD dependent (EC 1.2.1.12), has an Mr of 145,000 and subunits of Mr 37,000. It is dissociated to inactive dimers by ATP, whereas NAD+ in the presence of reductant promotes its reactivation. The amino acid composition is related to glyceraldehyde 3-phosphate dehydrogenases from animal sources and is most similar to pea seed glyceraldehyde 3-phosphate dehydrogenase. The enzyme exhibits a range of pI values from 5 to 7, but a second electrofocusing in the presence of dithioerythritol results in a single main form with pI 5.33, consistent with the behavior in polyacrylamide and cellulose acetate gel electrophoresis. Chloroplast NAD(P)-glyceraldehyde 3-phosphate dehydrogenase (EC 1.2.1.13) has been obtained from beet, pea, Ranunculus, Arum, and maize leaves. The stable form is an oligomer of about 800,000 Mr (±10%), while a minor, possibly damaged fraction elutes as a retarded peak from agarose columns. The Mr 800,000 form is reversibly dissociated to protomers of Mr 160,000 by NADP+, with increase of apparent NADP-dependent activity. Two subunits are present in similar amounts in all association states and after all treatments: α with Mr 36,000, and β with Mr 41,000. The form found in density gradient ultracentrifugation has an Mr of 390,000. Isoelectric points of the various forms lie between pH 4.1 and 4.7 for all species, with a main peak usually at pI 4.45. The amino acid composition of beet chloroplast glyceraldehyde phosphate dehydrogenase is not closely related to that of beet leaf NAD-dependent glyceraldehyde 3-phosphate dehydrogenase. © 1979.