DISTRIBUTION OF CHLOROPHYLLASE AMONG COMPONENTS OF CHLOROPLAST MEMBRANES IN CITRUS-SINENSIS ORGANS

Chlorophyllase (Chlase) (EC 3.1.1.14) catalyzes the removal of phytol chain from chlorophyll (Chl), which is one of the initial steps of the natural breakdown of Chl during senescence. Chlase has been assumed t o be a component of the thylakoid membranes. We have examined the asso ciation of Chlase with specific thylakoid Chl-protein complexes, using a non-denaturing Deriphat PAGE system (''green'' gels). Chl-protein m ulticomplexes of orange leaves were separated into photosystem I (PSI) , its core complex (CCI), oligomeric and monomeric forms of the light- harvesting complex of photosystem II (LHCIIo and LHCIIm), and a ''free pigment'' (FP) band. The separated complexes, as well as ''empty'' sp aces between them, were extracted from the gel, and Chlase activity wa s determined. Chlase activity was consistently found in proximity to t he LHCIIm; with some activity also present in a colourless zone, close to the front of LHCIIm. Little or no Chlase activity was detected in LHCIIo zone. Chlase activity of yellow orange fruit peel, which appare ntly does not contain Chl-protein components, also migrated to the sam e zone as that of young and mature leaves. Incubation of LHCIIo in the presence of detergents increased the LHCIIm but did not release more Chlase activity. In sucrose gradient separations Chlase activity was n ot confined to Chl-protein complexes and was detectable in other fract ions, including the plastid envelope fraction. Critical assessment of the data indicates that the comigration of Chlase activity with LHCIIm may be incidental and does not represent a real association of Chlase with Chl-protein complexes.