Comparisons of monoacylglycerols and diacylglycerols of varying fatty acid composition as substrates for the acylglycerol kinase(s) of rat brain

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Abstract
Asstract: The properties of diacylglycerol and monoacylglycerol kinase activities present in 90,000 x g pellet and 90,000 × g supernatant fractions from rat brain were examined and compared. Of the properties examined, time course (linear for 10 min), enzyme concentration, pH optimum (7.4–7.5), varying ATP (5 mM) and Mg2+ (10 mM) concentrations all showed similar optima for both activities. The optima for acylglycerol (5 mM for diacylglycerols; 3 mM for monoacylglycerols) and deoxycholate concentrations (0.1% for diacylglycerol kinase; 0.03% for monoacylglycerol kinase) differed slightly. Examination of the subcellular distribution for these activities also showed a similar pattern. All fractions showed significant activities, but the most was in the supernatant fraction. The similarities in properties and localization of the 2 kinase activities suggest a single enzyme may function. On this assumption, an extensive study using mono‐ and diacylglycerols of varying fatty acid composition gave the following results: (a) acylglycerols with the same fatty acid present showed increasing activity in the order: 1‐monoacylglycerol, 2‐monoacylglycerol and 1,2‐diacylglycerols; (b) when saturated fatty acids were present the order of decreasing activity varied directly with increasing chain length for C10→C20; (c) when one or more unsaturated fatty acids were present good activities resulted, but no clear pattern emerged, although acylglycerols with18∶1 and18∶3 fatty acids were more active than those with18∶2 and20∶4 fatty acids. These patterns do not support a role for this kinase in producing phosphatidic acids or lyso phosphatidic acids of the correct composition to act as precursors for the de novo synthesis of the predominant 1‐stearoyl, 2‐arachidonoyl molecular species of phosphatidylinositol.