WITH CHLOROPHYLL PIGMENTS FROM PROLAMELLAR BODIES TO LIGHT-HARVESTINGCOMPLEXES

The biosynthetic chain leading from 5-aminolevulinic acid to chlorophy ll is localised to the plastid. Many of the enzymes are nuclear-encode d. NADPH-protochlorophyllide oxidoreductase (EC 1.3.1.33) is one such enzyme which is encoded by two different genes and can exist in an A a nd a B form. Its import into the plastid seems to be facilitated when protochlorophyllide is present in the chloroplast envelope. Within the plastid the reductase is assembled to thylakoids or prolamellar bodie s. The specific properties of the reductase together with the specific properties of the lipids present in the etioplast inner membranes pro mote the formation of the three-dimensional regular network of the pro lamellar bodies. The reductase forms a ternary complex with protochlor ophyllide and NADPH that gives rise to different spectral forms of pro tochlorophyllide. Light transforms protochlorophyllide into chlorophyl lide and this photoreaction induces a conformational change in the red uctase protein which leads to a process of disaggregation of enzyme, p igment aggregates and membranes, which can be followed spectroscopical ly and with electron microscopy. The newly formed chlorophyllide is es terified by a membrane-bound nuclear-encoded chlorophyll synthase and the chlorophyll molecule is then associated with proteins into active pigment protein complexes in the photosynthetic machinery.