CHLOROPLAST BIOGENESIS 76 - REGULATION OF 4-VINYL REDUCTION DURING CONVERSION OF DIVINYL MG-PROTOPORPHYRIN-IX TO MONOVINYL PROTOCHLOROPHYLLIDE A IS CONTROLLED BY PLASTID MEMBRANE AND STROMAL FACTORS

Most of the chlorophyll (Chi) a of green plants is formed via two bios ynthetic routes, namely the carboxylic divinyl and monovinyl chlorophy ll biosynthetic routes. These two routes are linked by (4-vinyl) reduc tases that convert divinyl tetrapyrroles to monovinyl tetrapyrroles by reduction of the vinyl group at position four of the macrocycle to et hyl. The activities of these two routes are very sensitive to cell dis ruption. For example in barley leaves, cell disruption, a mandatory st ep during plastid isolation, results in partial inactivation of the ca rboxylic divinyl route, Investigations with subplastidic fractions rev ealed that the carboxylic divinyl and monovinyl biosynthetic routes we re regulated by a delicate interaction that involved plastid membranes , stroma, and reduced pyridine nucleotides. While the monovinyl biosyn thetic route was very active in isolated plastid membranes, activation of the divinyl biosynthetic route required the joint presence of plas tid membranes and stroma. Contrary to expectation, activity of the car boxylic divinyl biosynthetic route was greatly enhanced by addition of NADPH to the lysing buffer used during plastid membranes and stroma p reparation. NADPH in cooperation with the plastid stroma may play an i mportant regulatory role during the biosynthesis of divinyl and monovi nyl protochlorophyllide a.