Malonate, malonyl-coenzyme A, and acetyl-coenzyme A in developing rat brain.

Free malonate, malonyl-coenzyme A (malonyl-CoA), and acetyl-CoA were assayed in rat brain at developmental ages from the 20th day of gestation to 60 days of postnatal life. The determination of malonate was based on its conversion to malonyl-CoA and decarboxylation to acetyl-CoA by enzyme extracts from Pseudomonas fluorescens. The resulting acetyl-CoA reacted with [4-14C]oxaloacetate to form [5-14C]citrate, which was isolated by TLC. Malonyl-CoA in perchloric acid extracts from brain was converted to acetyl-CoA by rat liver mitochondrial malonyl-CoA decarboxylase (EC 4.1.1.9). Acetyl-CoA derived from this step was assayed by a modified CoA-cycling procedure. Brain acetyl-CoA was also assayed by CoA cycling. Prenatal brain contained no free malonate but malonyl-CoA was present. The acetyl-CoA level was relatively high just prior to birth and declined slightly with growth. Malonate concentrations after birth rose rapidly to reach 192 nmol/g wet weight at 60 days. Adult levels for malonyl-CoA and acetyl-CoA were 1.83 and 1.90 nmol/g wet weight, respectively. The origin and natural role of free malonate in brain are not known but deacylation of malonyl-CoA by reversal of the malonyl-CoA synthetase reaction is postulated. Rat liver and kidney also contain substantial concentrations of free malonate.