Inhibition by long-chain acyl-CoAs of glucose 6-phosphate metabolism in plastids isolated from developing embryos of oilseed rape (Brassica napus L.)

The effects of long-chain acyl-CoA (IcACoA) esters (both added exogenously and synthesized de novo) and acyl-CoA binding protein (ACBP) on plastidial glucose 6-phosphate (Glc6P) and pyruvate metabolism were examined using iso lated plastids. The binding of IcACoA esters by ACBP stimulated the utiliza tion of Glc6P for fatty acid synthesis, starch synthesis and reductant supp ly via the oxidative pentose phosphate (OPP) pathway. Stimulation occurred at low (1-10 mu M) concentrations of ACBP, Pyruvate-dependent fatty acid sy nthesis was not directly affected by ACBP. However, addition of ACBP did in crease the Glc6P-dependent stimulation of pyruvate utilization mediated thr ough the OPP pathway. On the basis of these experiments, we conclude that I cACoA esters may inhibit Glc6P uptake into plastids, and that this inhibiti on is relieved by ACBP. We also suggest that utilization of other substrate s for fatty acid synthesis may be affected by IcACoA/ACBP via their effects on the OPP pathway.