title: Covalent labelling of the NADPH: protochlorophyllide oxidoreductase from etioplast membranes with [3H]N-phenylmaleimide.
abstract: [3H]N-Phenylmaleimide has been used to covalently label in a specific manner the substrate-protected thiol groups of the enzyme protochlorophyllide reductase. In membrane preparations from oat (Avena sativa) and runner-bean (Phaseolus vulgaris) seedlings, two related peptides of mol.wts. 35000/37000 and 34000/35000 respectively and showing properties expected of the reductase have been identified, whereas the same technique with barley (Hordeum vulgare) extracts resulted in labelling a single peptide of mol.wt. 38000. Evidence is presented that both NADPH and protochlorophyllide are required for protection of the essential thiol groups on the reductase in oat extracts, a situation favouring a ternary complex as the structure for the photoactive enzyme--substrates intermediate.
mesh_terms: D002736:Chloroplasts / Q000201:enzymology*; D003624:Darkness; D003720:Densitometry; D002523:Edible Grain / Q000201:enzymology; D007425:Intracellular Membranes / Q000201:enzymology; D008301:Maleimides / Q000494:pharmacology*; D008970:Molecular Weight; D010088:Oxidoreductases / Q000037:antagonists & inhibitors*; D044925:Oxidoreductases Acting on CH-CH Group Donors; D010455:Peptides / Q000378:metabolism; D010779:Photofluorography; D014316:Tritium
chemical_list: D008301:Maleimides; D010455:Peptides; D014316:Tritium; C028525:N-phenylmaleimide; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase