Localization of chlorophyllase in the chloroplast envelope

Chlorophyllase catalyzes the first step in the catabolic pathway of chlorophyll. It is a constitutive enzyme located in chloroplast membranes. In isolated plastids the hydrolysis of the endogenous chlorophyll does not take place unless the membranes are solubilized in the presence of detergent. The structural latency of chlorophyllase activity appears to be due to the differential locations of substrate and enzyme within the plastids. Envelope membranes prepared from both chloroplasts and gerontoplasts contain chlorophyllase activity. The isolation of envelopes is associated with a marked increase in chlorophyllase activity per unit of protein. Yields of chlorophyllase and of specific envelope markers in the final preparations are similar, suggesting that the enzyme may be located in the envelope. It is hypothesized that the breakdown of chlorophyll during leaf senescence requires a mechanism that mediates the transfer of chlorophyll from the thylakoidal pigment-protein complexes to the sites of catabolic reactions in the envelope.