Mouse submaxillary gland renin contains a noncovalently attached fatty acid

Renin A from the submaxillary gland of male mice has been shown by a gas chromatography/mass spectrometry method to contain near stoichiometric amounts of a fatty acid mixture. The fatty acids on mouse renin were partially exchangeable with free tridecanoic acid in solution, with the tridecanoic acid truly exchanged and not just adsorbed in addition to the fatty acids already present. A gas chromatography/mass spectrometry analysis of the composition of the free fatty acids of the submaxillary gland of male mice showed that the mixture of fatty acids extracted from the gland was significantly different from the mixture of free fatty acids extracted from renin A. The renin-extracted fatty acids were relatively richer in saturated fatty acids, like myristic and palmitic acids, and poorer in polyunsaturated fatty acids, like linoleic and arachidonic acid, than the free fatty acids of the gland. The enzymatic activity of mouse renin was markedly stimulated by saturated fatty acids in 50 mM sodium acetate, pH 5.38, in a concentration-dependent, saturable manner. Palmitic acid stimulated renin activity versus synthetic tetradecapeptide renin substrate about 7-fold in this buffer, with half-maximal stimulation at 14 microM. Stearic and myristic acids also showed good stimulation but linoleic acid and ethyl myristate were much less effective at the stimulation. A possible physiological role for the loss of renin activity at acid pH due to loss of bound fatty acids would be to protect the mouse against internalized renin.