Effect of calcium deficiency on acyl-CoA synthetase activity in microsomes from various rat tissues.

The specific activity of long-chain acyl-CoA synthetase in microsomes from various tissues of control and calcium-deficient rats was determined. It was found that the saturated acids, palmitic and stearic, were preferential substrates compared to the non-saturated linoleic, alpha-linolenic and eicosa-8,11,14-trienoic acids. All of them showed similar Vm values with different affinity constants. After 60-day treatment on a calcium-deficient diet (0.5 g Ca/Kg diet), a significant increase in the acyl-CoA synthetase activity was observed for all the tested fatty acids in liver and kidney microsomes. These changes were evoked without any modification in the substrate selectivities shown for the control microsomes, and they were well-correlated with calcium level in both tissues. Under the calcium deficient state an increase in Vm values was observed for palmitic and eicosatrienoic acids with no changes in the corresponding Km, suggesting an increment in the number of active enzyme molecules within the microsomal membrane.