FUNCTIONAL MOLECULAR-MASS OF RAT HEPATIC LIPASE IN LIVER, ADRENAL-GLAND AND OVARY IS DIFFERENT

Lipoprotein lipase (LPL) is functionally active only as a dimer. It is also generally assumed that the highly homologous hepatic lipase func tions as a dimer, but no clear evidence has been presented. A hepatic lipase-like activity, also indicated as L-type lipase, is present in a drenal and ovary tissues. This enzyme is thought to originate from the liver and to be identical to hepatic lipase. We determined the functi onal molecular mass of hepatic lipase in rat liver, adrenal gland and ovary by radiation inactivation, a method for determining the function al size of a protein without the need of prior purification. Samples w ere exposed to ionizing radiation at -135 degrees C. Hepatic lipase ac tivity in liver homogenate showed a single exponential decay. The func tional molecular mass was calculated to be 63+/-10 kDa. Hepatic lipase activity in adrenal homogenate was found to have a functional molecul ar mass of 117+/-16 kDa. The functional molecular masses of the lipase s partially purified from rat liver perfusate, adrenal homogenate or o varian homogenate showed the same pattern, a target mass for the liver enzyme of 56+/-6 kDa and a target mass of 117+/-14 kDa for the enzyme from adrenal gland or ovary. In Western blot analysis the mass of the structural units of hepatic lipase in liver was 57 kDa and in adrenal and ovary tissue 51 kDa. We conclude that the functional unit of hepa tic lipase in the liver is a monomer. The enzyme in adrenal gland and ovary is different from the liver and the functional unit may be a dim er.