Biosynthesis of phytyl side-chain of chlorophyll a: apparent reutilization of carbon dioxide evolved during acetate assimilation in biosynthesis of chloroplastidic isoprenoid

Abstract

Equal incorporation of either acetyl methyl or carboxy carbons into all carbon atoms of the phytyl side-chain of chlorophyll via doubly labelled acetyl CoA, with complete loss of methyl hydrogens, indicated that CO₂ evolved from the carboxy carbon during acetate assimilation through the TCA cycle may be reutilized via the reductive pentose phosphate cycle followed by the glycolic pathway, while incorporation of [2-¹³C]glycerol and [6,6-²H₂]glucose into the phytyl chain demonstrated the simultaneous operation of two distinct pathways, both the mevalonate pathway and the 1-deoxy-D-xylulose mediating pathways (non-mevalonate pathway) in isopentenyl diphosphate formation within liverwort chloroplasts.