BIOSYNTHESIS OF PHYTYL SIDE-CHAIN OF CHLOROPHYLL-A - APPARENT REUTILIZATION OF CARBON-DIOXIDE EVOLVED DURING ACETATE ASSIMILATION IN BIOSYNTHESIS OF CHLOROPLASTIDIC ISOPRENOID

Equal incorporation of either acetyl methyl or carboxy carbons into al l carbon atoms of the phytyl side-chain of chlorophyll via doubly labe lled acetyl CoA, with complete loss of methyl hydrogens, indicated tha t CO2 evolved from the carboxy carbon during acetate assimilation thro ugh the TCA cycle may be reutilized via the reductive pentose phosphat e cycle followed by the glycolic pathway, while incorporation of [2-C- 13]glycerol and [6,6-H-2(2)]glucose into the phytyl chain demonstrated the simultaneous operation of two distinct pathways, both the mevalon ate pathway and the 1-deoxy-D-xylulose mediating pathways (non-mevalon ate pathway) in isopentenyl diphosphate formation within liverwort chl oroplasts.