Effect of polyamines on palmitoyl-coenzyme A-caused inhibition of glucose-6-phosphate dehydrogenase from baker's yeast

Abstract

Aliphatic polyamines reversed the inhibition of baker's yeast glucose-6-phosphate dehydrogenase by palmitoyl-CoA. The reversal effects of the polyamines on the inhibition were related not only to the number of amino (imino) groups but also to the carbon chain length of polyamine. The relieving constant ( K r ) was calculated to determine the absolute concentration of each examined polyamine required to relieve the enzyme from the inhibition. A smaller K r value indicates a stronger relieving activity. An ethylamine derivative with a large number of amino groups was more effective in reversing the palmitoyl-CoA inhibition. The K r values of long-chain aliphatic diamines, triamines, and tetramines were smaller than those of short-chain ones. However, n-butylamine and ornithine, composed of four carbons like putrescine, had markedly larger K r values than putrescine. Substitution of one or two amino groups by carboxyl or hydroxyl groups also appeared to relieve the enzyme from the inhibition. These results suggest that the reversal effect on palmitoyl-CoA inhibition is one of the important roles of polyamines. Furthermore, it is possible that the interaction of palmitoyl-CoA and polyamines physiologically regulates the pentose monophosphate cycle in baker's yeast.