K. Schoonderwoerd et al., FUNCTIONAL MOLECULAR-MASS OF RAT HEPATIC LIPASE IN LIVER, ADRENAL-GLAND AND OVARY IS DIFFERENT, Biochemical journal, 318, 1996, pp. 463-467
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.