Quaternary Structure of Higher Plant Glyceraldehyde‐3‐Phosphate Dehydrogenases

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Abstract
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 3 plant spp. contains 2 separate isoenzymes. Isoenzyme 1 (fast moving during conventional electrophoresis) precipitates with the ammonium sulfate fraction 55-70% saturation. It shows 2 separate subunits in dodecyl sulfate 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 MW as subunit A in isoenzyme 1 and is apparently a tetramer (A4). The MW of subunits A/B for spinach, peas and barley were determined as 38,000/40,000, 38,000/42,000 and 36,000/39,000, respectively. The NAD-specific glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12) was purified from S. oleracea and P. sativum by affinity chromatography on blue Sepharose CL-6B. The enzyme from both plant species is a tetramer of subunits with MW 39,000. The present findings contrast with heterogeneous results obtained previously. Apparently there are considerable interspecific differences in the quaternary structure of glyceraldehyde-3-phosphate dehydrogenases from higher plants.