malonyl-CoA Synthetase Research Articles

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.

Developmental changes in malonate-related enzymes of rat brain

Mitochondria and high-speed supernatant were prepared from rat brain homogenates at 0–50 days of age. The development of malonyl-CoA synthetase, malonyl-CoA decarboxylase, coenzyme A-transferases and acetyl-CoA hydrolase was examined and compared to de novo fatty acid biosynthesis. The specific activity of malonyl-CoA synthetase rose steeply between 6 and 10 days, and this sudden increase coincided with peak specific activity of fatty acid synthetase. Similarly, malonate activation by coenzyme A-transfer from succinyl-CoA increased rapidly at the same time. Transfer of the coenzyme A moiety from acetoacetyl-CoA was only minimal during this period. Brain mitochondria had active malonyl-CoA decarboxylase which showed an almost linear increase of specific activity between 0 and 50 days. Acetyl-CoA resulting from malonyl-CoA decarboxylation underwent enzymatic hydrolysis to acetate and free coenzyme A. Only traces of acetoacetate were recovered. In mitochondria, acetyl-CoA hydrolase increased progressively whereas the cytosolic enzyme had high specific activity at birth which declined slowly during maturation.

Fat metabolism in higher plants: XXI. Biosynthesis of fatty acids by avocado mesocarp enzyme systems

1. 1. In the avocado mesocarp, both the particulate and the supernatant fractions readily synthesize long-chain fatty acid from suitable substrates. The particulate fraction can utilize effectively acetate, acetyl-CoA and malonyl-CoA but malonic acid is inactive. The supernatant fraction can only utilize malonyl-CoA or malonic acid. Data indicate that acetyl-CoA carboxylase (acetyl-CoA: CO 2 ligase (ADP), EC 6.4.1.2) is present in the particulate fraction but absent in the supernatant while the convere is true for malonyl-CoA synthetase (malonate: CoA ligase (AMP)). 2. 2. The supernatant fraction synthesizes only palmitic and stearic acids, mainly in the form of glycerides. Unsaturated fatty acid synthesis is associated with the particulate fraction. Possible factors controlling the extent of C 16 and C 18 fatty acids in these systems are discussed.