Bernbäck S, Hernell O, Bläckberg L
Department of Physiological Chemistry, University of Umeå, Sweden.
Biochim Biophys Acta. 1987 Nov 21;922(2):206-13. doi: 10.1016/0005-2760(87)90156-1.
Preduodenal lipolysis is considered to promote efficient lipid digestion in the neonatal period. The lipase(s) responsible may be of pregastric or gastric origin depending upon the species. We have previously reported on purification and molecular characterization of a pregastric lipase from calf. Antibodies to this bovine enzyme crossreact with a protein of similar size in human gastric contents and also inhibit its lipolytic activity. Since the bovine and human enzymes also have similar kinetic properties, the view is favoured that the bovine enzyme can be used as a model for physiological studies relevant to human neonates. In contrast to the lipases operating in the small intestine pregastric lipase has the unique property of initiating the hydrolysis of human milk fat globule triacylglycerol. In order to do this no cofactor is required. Pregastric lipase was stable at low pH and had an acid-pH optimum. Furthermore, it was extremely resistant to pepsin. In contrast, pancreatic proteinases, i.e. trypsin and chymotrypsin, inactivated the enzyme. The rate of inactivation was increased in the presence of bile salts which by themselves could inhibit enzyme activity. Thus, pregastric lipase is ideally suited for activity in the stomach but will not, under healthy conditions, contribute to lipid digestion in the duodenum.
十二指肠前脂肪分解被认为可促进新生儿期的高效脂质消化。根据物种不同，负责该过程的脂肪酶可能源自胃前或胃。我们之前报道过从犊牛中纯化胃前脂肪酶及其分子特征。针对这种牛酶的抗体与人胃内容物中大小相似的一种蛋白质发生交叉反应，并且还抑制其脂解活性。由于牛和人酶也具有相似的动力学特性，因此倾向于认为牛酶可作为与人类新生儿相关的生理学研究模型。与在小肠中起作用的脂肪酶不同，胃前脂肪酶具有启动人乳脂肪球三酰甘油水解的独特特性。为此不需要辅因子。胃前脂肪酶在低pH下稳定，且最适pH为酸性。此外，它对胃蛋白酶具有极强的抗性。相反，胰蛋白酶即胰蛋白酶和糜蛋白酶可使该酶失活。在胆汁盐存在下失活速率增加，而胆汁盐本身可抑制酶活性。因此，胃前脂肪酶非常适合在胃中发挥活性，但在健康状况下不会对十二指肠中的脂质消化产生作用。
