Protochlorophyllide b does not occur in barley etioplasts

Barley (Hordeum vulgare L.) etioplasts were isolated, and the pigments mere extracted with acetone, The extract was analyzed by HPLC. Only protochloro phyllide a and no protochlorophyllide b was detected (limit of detection <1 % of protochlorophyllide a). Protochlorophyllide b was synthesized starting from chlorophyll b and incubated with etioplast membranes and NADPH, In th e light, photoconversion to chlorophyllide b was observed, apparently catal yzed by NADPH:protochlorophyllide oxidoreductase. In darkness, reduction of the analogue zinc protopheophorbide b to zinc 7(1)-hydroxy-protopheophorbi de a was observed, apparently catalyzed by chlorophyll b reductase. We conc lude that protochlorophyllide b does not occur in detectable amounts in eti oplasts, and even traces of it as the free pigment are metabolically unstab le. Thus the direct experimental evidence contradicts the idea by Reinbothe et al, (Nature 397 (1999) 80-84) of a protochlorophyllide b-containing lig ht-harvesting complex in barley etioplasts. (C) 1999 Federation of European Biochemical Societies.