Circulating and liver-bound salt-resistant hepatic lipases in the golden hamster.

The serum of male golden hamsters was found to contain a circulating triacylglycerol hydrolase activity (serum lipase). In vitro, the enzyme activity was slightly activated by 1 M NaCl (+20%) and inhibited by rat serum (-29%). The hamster liver contained an enzyme with similar characteristics (liver lipase). This enzyme was released into the circulation after intravenous administration of heparin. Both lipase activities were further characterized and compared. The serum lipase had a pH optimum of 9, which was higher than that of the liver enzyme (pH 8.0). The serum enzyme did not bind to Sepharose-heparin columns in contrast to the liver lipase, which could be eluted from the column with 0.75 M NaCl. A polyclonal antibody preparation raised against the heparin-releasable salt-resistant lipase from rat liver inhibited both the hamster serum enzyme and the liver enzyme completely. The affinity of the antibodies towards the hamster enzymes was lower than the affinity towards the rat liver enzyme, but similar with that towards the hamster enzymes in the serum and the liver. A panel of five monoclonal antibodies raised against the rat enzyme did not bind either of the hamster enzymes. If the hamsters were fed a normal lab chow, the lipase activity in the serum amounted up to 110 +/- 20 mU (mean +/- S.D., n = 16) per ml serum (about 600 mU per animal), the liver contained 200 +/- 41 mU per g tissue (total about 800 mU per animal). In animals fed a cholesterol-enriched diet, the serum activity increased by 82% and the liver activity by 27%.

Application of heparin-conjugated Sepharose for the measurement of cobalamin-saturated and unsaturated transcobalamin II.

The cobalamin-binding plasma protein transcobalamin II has a high affinity for the anticoagulant heparin. This phenomenon has been exploited in a new method for the quantification of cobalamin-saturated (holo-) and unsaturated (apo-) transcobalamin II in human plasma. Transcobalamin II is adsorbed from human plasma to heparin-conjugated Sepharose under suitable conditions and either cobalamin from adsorbed holo-transcobalamin II is measured by a radioisotope dilution assay or apo-transcobalamin II is determined by measuring the adsorbed unsaturated cobalamin-binding capacity with radioactive cobalamin. The assay results for apo- and holo-transcobalamin II are similar (r = 0.99 and 1.0, respectively) to those obtained with the established radioimmunosorbent assay using specific rabbit anti-human transcobalamin II-conjugated Sepharose. The assay cannot be carried out in heparin-anticoagulated plasma, because the free heparin competes with the immobilized heparin for the binding of transcobalamin II. The amount of heparin in plasma from patients being treated with subcutaneous or intravenous heparin is too low to interfere significantly with the measurement of transcobalamin II. Also the presence of circulating anti-transcobalamin II antibodies, as occur in some rare patients after frequent intramuscular injections of cobalamin, does not influence the assay.