CHLOROPLAST BIOGENESIS-72 - A [4-VINYL]CHLOROPHYLLIDE-ALPHA REDUCTASEASSAY USING DIVINYL CHLOROPHYLLIDE-ALPHA AS AN EXOGENOUS SUBSTRATE

[4-Vinyl] Chlorophyllide a reductase (4VCR) catalyzes the the conversi on of 2,4-divinyl chlorophyllide a (DV Chlide a) to 2-vinyl,4-ethyl ch lorophyllide a (MV Chlide a) via an NADPH-dependent reaction. MV Chlid e a is the immediate precursor of monovinyl chlorophyll a in plants. I n etiolated cucumber (Cucumis sativus L.) cotyledons, 4VCR is a plasti dic membrane-bound enzyme, Further research on this enzyme required th e development of an assay that utilizes DV Chlide a as an exogenous su bstrate. Such an assay is now described. It involves conversion of exo genous DV Chlide a to MV Chlide a at high rates by etioplast membranes of cucumber, corn (Zea mays L.), and barley (Hordeum vulgare L.). 4VC R exhibits high activity between 30 and 40 degrees C and in the pH ran ge of 6.3 to 7.0, Activity is quasilinear for the first 60 s of incuba tion. (C) 1995 Academic Press, Inc.