Role of Monoglyceride Hydrolase in Lipoprotein Triglyceride Catabolism
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概要
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Post-heparin plasma has been shown to contain several enzymes, that is, lipoprotein lipase, hepatic triglyceride lipase, monoglyceride hydrolase, phospholipase and so on. Little is known, however, in the physiological roles of these enzymes in the catabolism of lipoprotein triglyceride. The present study was designed to help elucidate the physiological roles of monoglyceride hydrolase in the catabolic reaction of lipoprotein triglyceride.<BR>The monoglyceride hydrolase activity was inhibited progressively with increasing amounts of serum added. However, in the case of preincubation of serum with the enzyme, the inhibitions were more slightly than those with substrate. At lower concentrations bovine serum albumin slightly activated the enzyme activity, whereas at higher concentrations it caused the significant inhibition. Subsequently, the effects of apolipoproteins on the monoglyceride hydrolase activity were investigated. In the cases of apoLp C-I, C-II and C-III, the enzyme activity was activated in the preincubation of the apolipoproteins with the enzyme, whereas without effect with the substrate. On the other hand, in the cases of apo-LDL and -HDL, the enzyme activity was inhibited in the both preincubation conditions.<BR>Triglyceride hydrolysis by lipoprotein lipase has been shown in vitro to be activated by apoLp C-II and inhibited by apoLp <I>In vitro</I> evidences also indicated that the inhibition was related to the apoLp C-III-triglyceride ratio. Hydrolysis of triglyceride in VLDL would result in inhibitory levels of the apoLp C-III on a given lipoprotein unless there is a mechanism for removal of apoLp C-III from the lipoprotein or for blocking in its inhibitory activity. Brown and Baginsky suggested that monoglyceride could act in the blocking of apoLp C-III inhibition of lipoprotein lipase reaction, and that the interaction of monoglyceride with apoLp C-III could produce a complex which left the surface of the VLDL. On the other hand, the possibility of monoglyceride hydrolase forming a complex with apoLp C-III has been suggested by the present results. The present results also suggested that the monoglyceride-apoLp C-III complex was as active as monoglyceride alone for the substrate of monoglyceride hydrolase, and that the monoglyceride hydrolase-apoLp C-III complex reacted as the activated-form of the monoglyceride hydrolase. In summary, monoglyceride hydrolase also act as one of the blocking agents for the apoLp C-III inhibition of lipoprotein lipase activity.
- Japan Society of Clinical Chemistryの論文
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