A LIGHT-INDUCED PROTEASE FROM BARLEY PLASTIDS DEGRADES NADPH, PROTOCHLOROPHYLLIDE OXIDOREDUCTASE COMPLEXED WITH CHLOROPHYLLIDE

The NADPH:protochlorophyllide oxidoreductase precursor protein (pPorA) of barley (Hordeum vulgare L. cv. Carina), synthesized from a full-le ngth cDNA clone by coupling in vitro transcription and translation, is a catalytically active protein, It converts protochlorophyllide to ch lorophyllide in a light- and NADPH-dependent manner. At least the pigm ent product of catalysis remains tightly bound to the precursor protei n. The chlorophyllide-pPorA complex differs markedly from the protochl orophyllide-pPorA complex: with respect to sensitivity to attack by a light-induced, nucleus-encoded, and energy-dependent protease activity of barley plastids, The pPorA-chlorophyllide complex is rapidly degra ded, in contrast to pPorA-protochlorophyllide complexes containing or lacking NADPH, which are both resistant to protease treatment, Unexpec tedly, pPorA devoid of its substrates or products mas less sensitive t o proteolysis than the pPorA-chlorophyllide complex, suggesting that b oth substrate binding and product formation during catalysis had cause d differential changes in protein conformation.