Control of hepatic mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase during the foetal/neonatal transition, suckling and weaning in the rat
Correspondence to P. A. Quant, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambidge CB2 1QW, England
- 1We assayed active and total (i.e. active plus succinylated) 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase in mitochondria isolated from foetal, neonatal, suckling or weaned rats.
- 2HMG-CoA synthase was substantially succinylated and inactivated in mitochondria isolated from termfoetal, (1-h-old, 6-h-old, 1-day-old) neonatal, suckling and high carbohydrate/low-fat (hc)-weaned rats. Succinylation of HMG-CoA synthase was very low in mitochondria isolated from the livers of foetal, 30-min-old neonatal and high-fat/carbohydrate-free (hf)-weaned rats.
- 3There was a negative correlation between active HMG-CoA synthase and succinyl-CoA content in mitochondria isolated from term-foetal, suckling and hc-weaned rats.
- 4Differences in active enzyme could not be entirely accounted for by differences in succinylation and inactivation of the synthase. Immunoassay confirmed that the absolute amounts of mitochondrial HMG-CoA synthase increased during the foetal/neonatal transition and decreased with hc weaning. The levels remained elevated with hf weaning.
- 5From these data we propose that mitochondrial HMG-CoA synthase is controlled by two different mechanisms in young rats. Regulation by succinylation provides a mechanism for rapid modification of existing enzyme in response to changing metabolic states. Changes in the absolute amounts of HMG-CoA synthase provide a more long-term control in response to nutritional changes.