Studies on triglyceride lipases from rat adipose tissue

Effect of prolactin (PRL) on lipoprotein lipase (LPL) activity in the rat fetal liver

In order to clarify the possible involvement of PRL in the regulation of lipid metabolism, the influence of PRL on the levels of LPL activity in rat fetal liver was investigated. Rat fetuses at 18th day of gestation in one uterine horn were injected with o-PRL while those in the opposite horn with saline. Forty-eight hr later, the livers were removed from the fetuses, homogenized, defatted, dried overnight, and further homogenized to the enzyme suspension. The measurement of LPL activity in these suspensions revealed that LPL activity in the fetal liver treated with o-PRL was significantly higher than that of control. LPL activities in the rat fetal liver gradually increased until the time of birth as the gestation proceeded. These results suggest that PRL may be one of the factors regulating fetal lipid metabolism.

Congenital generalized lipodystrophy with insulin-resistant diabetes

Hyperglycemia, glucose intolerance, hyperinsulinemia and resistance to exogenous insulin were found in a 10-year-old Japanese boy diagnosed as having congenital generalized lipodystrophy. Studies on insulin receptors of circulating mononuclear leucocytes indicated that insulin-resistant diabetes combined with congenital generalized lipodystrophy may be due to disturbance of insulin binding to membrane receptors. No insulin-binding antibody or antibody that impairs insulin-receptor binding was found. Plasma glucagon showed an exaggerated response to L-arginine before treatment. After treatment with a controlled diet and an oral sulfonylurea (500 mg/day) for 4 weeks, there was improvement in the plasma glucagon response to L-arginine. Improvement in the hyperglycemia, hyperinsulinemia and acanthosis nigricans was also observed. On the other hand, on completion of a 7-day high-fat diet, a marked increase in serum free fatty acids, triglycerides and beta-lipoproteins was observed. The total plasma post-heparin lipolytic activity during the high fat diet was within the normal range. However, the level of protamine-inactivated activity was 3 times that of the control.

Partial purification and characterization of a triacyglycerol lipase from rat liver cytosol

A triacyglycerol lipase (EC 3.1.1.3) was purifiec about 60-fold from rat liver cytosol by delipidation with acetone and ethyl ether, hydroxyapatitie and Sephadex G-100 column chromatographies and isoelectrofocusing electrophoresis. The partially purified enzyme had a molecular weight of approximately 42 000 and an isolectric point of 7.2. The Km for trioleylglycerol was 0.33 mM and the pH optimum was around 8.0. The activity of the enzyme was not dependent on serum lipoproteins, but was stimulated about 2-fold by several proteins such as serum albumin, lipoproteins, gamma-globulin and ovalbumin. The lipase hydrolyzed trioleyglycerol to oleic acid and glycerol. NaCl had no effect on the enzymatic activity. Some physical and kinetic properties of the partially purified lipid-free lipase were different from those of crude non-delipidated lipase and also from those of a neutral triacylglycerol lipase which was recently purified partially from pig liver cytosol (Ledford, J.H. and Alaupovic, P. (1975) Biochim. Biophys. Acta 398, 132-148).