Purification and properties of an acid lipase from human gastric juice

An acid lipase (EC 3.1.1.3) from human gastric juice was purified by using poly(ethylene glycol)-6000 precipitation, ethanol fractionation and Sephadex G-75 gel filtration. A molecular weight of 44000 was obtained by SDS-polyacrylamide gel electrophoresis. pH-dependent aggregation was observed and by using Sephadex G-200 gel filtration, a molecular weight of 90000 was obtained at pH 6.0 and 45000 at pH 3.0, for the purified enzyme. A pH optimum of 5.3 was obtained using triolein as substrate. The apparent Km for tributyrin and triolein was found to be 21 and 73 mumol, respectively. Diacylglycerol and free fatty acids were the major hydrolytic end products of this enzyme. Studies on the positional specificity of the enzyme showed that the preferred site of hydrolysis was sn-3 and sn-1, although a good percentage of the sn-2 position was also hydrolysed. Conjugated bile salts inhibited the enzyme when triolein was used as substrate, whereas they activated it when tributyrin was used. Some of the properties of the purified human gastric juice acid lipase resembles those of rat and human lingual lipase.