ALTERED MONOVINYL AND DIVINYL PROTOCHLOROPHYLLIDE POOLS IN BCHJ MUTANTS OF RHODOBACTER-CAPSULATUS - POSSIBLE MONOVINYL SUBSTRATE DISCRIMINATION OF LIGHT-INDEPENDENT PROTOCHLOROPHYLLIDE REDUCTASE

In land plants in particular, it has been well established that chloro phyll intermediates, Mg-protoporphyrin, Mg-protoporphyrin monomethyles ter, protochlorophyllide, and chlorophyllide occur as monovinyl and di vinyl forms, The pool of monovinyl and divinyl intermediates differ ac cording to species, age of tissue, and light regime, In this study, we investigated the monovinyl and divinyl characteristics of protochloro phyllide and chlorophyllide in the purple non-sulfur photosynthetic eu bacterium Rhodobacter capsulatus. Our results indicate that mutations in genes known to completely block the reduction of protochlorophyllid e to chlorophyllide (such as bchN, bchB, and bchL mutants), accumulate a pool of monovinyl and divinyl forms of protochlorophyllide just as observed in plants, However, we also observed that directed insertion and deletion mutations in bchJ, a gene located in the photosynthesis g ene cluster, affected the ratio of monovinyl and divinyl protochloroph yllide, Specifically, bchJ-disrupted strains accumulate reduced levels of bacteriochlorophyll concomitant with the accumulation of divinyl p rotochlorophyllide, Mutants of bchJ in combination with a second mutat ion in bchL still produce a mixed pool of monovinyl and divinyl protoc hlorophyllide; however, the ratio of monovinyl to divinyl protochlorop hyllide is skewed in favor of divinyl protochlorophyllide. These resul ts thus identify bchJ as the first sequenced gene that affects the div inyl to monovinyl ratio of photopigment intermediates in any photosynt hetic organism, In addition, the results of our study also suggest tha t light-independent protochlorophyllide reductase is discriminatory fo r a monovinyl substrate.