Quaternary Structure of Higher Plant Glyceraldehyde‐3‐Phosphate Dehydrogenases

NAD(P)+‐induced changes in the aggregational state of prepurified NADP‐linked glyceraldehyde‐3‐phosphate dehydrogenase (EC 1.2.1.13) were used to isolate the enzyme from Spinacia oleracea, Pisum sativum and Hordeum vulgare. Each of the three plant species contains two separate isoenzymes. Isoenzyme 1 (fast moving during conventional electrophoresis) precipitates with the ammonium sulfate fraction 55–70% saturation. It shows two separate subunits in dodecylsulfate gels, which are probably arranged as A2B2 in the native enzyme molecule. Isoenzyme 2 (slow moving during conventional electrophoresis) precipitates with the ammonium sulfate fraction 70–95%. It contains a single subunit of the same Mr as subunit A in isoenzyme 1 and is apparently a tetramer (A4). The molecular weights of subunits A/B for spinach, peas and barley were determined as 38000/40000, 38000/42000 and 36000/39000 respectively. The NAD‐specific glyceraldehyde‐3‐phosphate dehydrogenase (EC 1.2.1.12) was purified from Spinacia oleracea and Pisum sativum by affinity chromatography on blue Sepharose CL‐6B. The enzyme from both plant species is shown to be a tetramer of subunits with Mr 39000. The present findings cont