Molecular heterogeneity of ferredoxin-NADP+ reductase from spinach leaves

Highly purified ferredoxin-NADP+ reductase from spinach leaves showed at least eight different protein bands in the electrofocused gel. All of them were catalytically active and were adsorbed on a ferredoxin-Sepharose 4B affinity column. The N-terminal amino acid sequence of the main component species was analyzed by the automatic Edman degradation method. It was found that when the reductase was stored at 4 degrees C, new protein bands appeared in isoelectric focusing and sodium dodecyl sulfate polyacrylamide gel electrophoreses, but the appearance of the bands was suppressed by the addition of a protease inhibitor, diisopropyl fluorophosphate. This indicates that the molecular heterogeneity of the reductase may result from the digestion with a protease present in spinach leaves.