In vitro and in vivo regulation of chloroplast glyceraldehydes‐3‐phosphate dehydrogenase isozymes from Chenopodium rubrum. I. Purification and properties of isozymes

Chloroplast glyceraldehyde‐3‐phosphate dehydrogenase (GPD, EC 1.2.1.13) was purified from leaves of Chenopodium rubrum L. Aggregated (≥ 10 6 ) and disaggregated (165 × 10 3 ) molecular weight forms were obtained by gel filtration in the presence of NAD + and NADP + , respectively. The disaggregated enzyme was separated into two isozymes by inverse ammonium sulphate gradient solubilization: “NADP‐GPD I” was homotetrameric (subunit molecular weight 39 × 10 3 ); “NADP‐GPD II” was heterotetrameric (subunit molecular weights 39 × 10 3 and 43 × 10 3 ). Isoelectric focusing of the isozymes, both aggregated and disaggregated, revealed two isoelectric forms in each case, at 4.3 and 7.7. Chloroplast GPD was “NADP‐suppressed” in crude extracts due to partial oxidation, incubation with dithioerythritol restored full activity.