Horm Metab Res 1974; 6(4): 247-255
DOI: 10.1055/s-0028-1093861
Originals

© Georg Thieme Verlag KG Stuttgart · New York

The Role of Calcium in Insulin Action - I. Purification and properties of enzymes regulating lipolysis in human adipose tissue: effects of cyclic-AMP and calcium ions[*]

A. H. Kissebah , N.  Vydelingum , B. R. Tulloch , H.  Hope-Gill , T. R. Fraser
  • Endocrine Unit, Department of Medicine, Royal Postgraduate Medical School, London, England
Further Information

Publication History

Publication Date:
08 January 2009 (online)

Abstract

The reaction steps involved in the activation and inactivation of the hormone sensitive lipase have been studied in human adipose tissue.

Homogenates prepared from adipose tissue shreds or isolated fat cells contained a cyclic-AMP dependant protein kinase. This enzyme was partially purified from the 100,000 g supernatant using DEAE Cellulose Column Chromatography. The activity of the purified preparation was stimulated 3-4 fold with cyclic-AMP and inhibited with progressive increases in free calcium concentration in the reaction mixture. Calcium seems to inhibit the binding of cyclic-AMP to the protein kinase regulatory units and thus abolishes cyclic-AMP stimulation.

In the presence of cyclic-AMP and ATP the protein kinase phosphorylates a lipase preparation partially purified from the same tissue with synchronous increase in the lipolytic activity. Inactivation of the lipase is preceeded by its dephosphorylation by a phosphatase(s) which is present in 105,000 g supernatant.

Increasing free calcium concentration between 10-8 and 10-3M produced progressive inhibition of the lipase activity. This inhibition can be attributed to a dual mechanism. First, calcium ions inhibited the protein kinase activation of the lipase. Second, calcium ions stimulated the adipose tissue phosphatase(s) and this increased the rate of inactivation of the hormone sensitive lipase.

A role for calcium ions as well as cyclic-AMP in the control of lipolysis is postulated.

1 Presented in part to European Association for the study of diabetes, Madrid, 6-8 September 1972

1 Presented in part to European Association for the study of diabetes, Madrid, 6-8 September 1972

    >