LOCALIZATION OF CHLOROPHYLLASE IN THE CHLOROPLAST ENVELOPE

Chlorophyllase catalyzes the first step in the catabolic pathway of ch lorophyll. It is a constitutive enzyme located in chloroplast membrane s. In isolated plastids the hydrolysis of the endogenous chlorophyll d oes not take place unless the membranes are solubilized in the presenc e of detergent. The structural latency of chlorophyllase activity appe ars to be due to the differential locations of substrate and enzyme wi thin the plastids. Envelope membranes prepared from both chloroplasts and gerontoplasts contain chlorophyllase activity. The isolation of en velopes is associated with a marked increase in chlorophyllase activit y per unit of protein. Yields of chlorophyllase and of specific envelo pe markers in the final preparations are similar, suggesting that the enzyme may be located in the envelope. It is hypothesized that the bre akdown of chlorophyll during leaf senescence requires a mechanism that mediates the transfer of chlorophyll from the thylakoidal pigment-pro tein complexes to the sites of catabolic reactions in the envelope.