Phospholipid modulation of low-Km cyclic AMP phosphodiesterase activity on rat adipocyte microsomes |
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Authors: | S L Macaulay F L Kiechle L Jarett |
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Affiliation: | Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104 U.S.A. |
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Abstract: | The ability of nine phospholipids to alter the activity of low-Km cyclic AMP phosphodiesterase was examined in microsomal fractions of rat adipocytes. The enzyme was activated by phosphatidylserine (21% at 300 microM) and phosphatidylglycerol (36% at 300 microM). The activation was concentration dependent over the range 1-1000 microM. Six other phospholipids were without effect. Phosphatidylinositol 4-phosphate inhibited the activity of the enzyme over the same range of concentrations (26% at 300 microM). Phosphatidylserine also activated a partially purified preparation of the enzyme, whereas phosphatidylinositol 4-phosphate was ineffective. The mechanism of the activation of the enzyme by phosphatidylserine and phosphatidylglycerol involved an increase in the apparent Vmax of the enzyme, while the inhibition by phosphatidylinositol 4-phosphate was associated with an increase in the Km of the enzyme for substrate. The phospholipid modulators of low-Km cyclic AMP phosphodiesterase activity did not alter the activity of high-Km cyclic AMP phosphodiesterase. The ability of phospholipids to alter the activity of low-Km cyclic AMP phosphodiesterase in native membranes suggests a possible role for phospholipids in metabolic regulation. |
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Keywords: | To whom correspondence and reprint requests should be addressed. Department of Pathology and Laboratory Medicine University of Pennsylvania School of Medicine Box 671 3400 Spruce Street/G1 Philadelphia Pa. 19104. |
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