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Inactivation of Hormone-sensitive Lipase from Adipose Tissue with Adenosine Triphosphate, Magnesium, and Ascorbic Acid

Su-Chen Tsai 1, Henry M. Fales 1, and Martha Vaughan 1

From the 1 From the Molecular Disease Branch and Laboratory of Chemistry, National Heart and Lung Institute, National Institutes of Health, Bethesda, Maryland 20014

Inactivation of ammonium sulfate-precipitated lipase requires, in addition to ATP and Mg2+ion, a dialyzable factor present in homogenates of adipose tissue (Tsai, S.-C., and Vaughan, M. (1972) J. Biol. Chem. 247, 6253–6258) and liver which has now been identified as ascorbic acid. It was extracted from acetone powder of rat liver with methanol-water, 70:30, and purified using barium precipitation and ion exchange and paper chromatography. Approximately 3 mg of a fine white powder obtained from 100 g of liver were used for preparation of trimethylsilyl and deuterotrimethylsilyl derivatives with and without prior reaction with diazomethane. Analysis of these with gas chromatography and mass spectrometry led to the conclusion that the factor was ascorbic acid. This was confirmed by analysis of the trimethylsilyl derivative of authentic l-ascorbic acid. The ultraviolet absorption spectrum and chemical characteristics of the isolated material were consistent with this designation.

Lipase inactivation was proportional to ascorbic acid concentration in the range of 0.3 to 3 µm in the presence of 2 mm ATP and 4 mm MgCl2. In the absence of the latter, ascorbic acid, like the inactivation factor, did not alter lipase activity. Identification of ascorbic acid as the tissue factor required for Mg2+ATP-dependent inactivation of the hormone-sensitive lipase should facilitate further characterization of this process. In addition, because the requirement for ascorbic acid appears to be rather specific and the effective concentrations low relative to those employed in many other enzymatic systems, these observations may lead to the demonstration of a role for ascorbic acid in reactions of a type not hitherto associated with this compound.

Submitted on March 29, 1973


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