Kamei A
Department of Biochemistry, Faculty of Pharmaceutical Sciences, Meijo University, Nagoya, Japan.
Biol Pharm Bull. 1996 Sep;19(9):1223-6. doi: 10.1248/bpb.19.1223.
Two fractions of esterase were partially purified from the soluble fraction of normal human lens. The apparent molecular masses of these enzymes were approximately 200 kDa (esterase-I) and 30 kDa (esterase-II). The optimal pH of esterase-I and esterase-II was 6.0 and 7.5, and their respective optimal temperature were 43 degrees C and 46 degrees C. The K(m) values of esterase-I and esterase-II for 4-methylumbelliferyl-palmitate were 0.14 and 0.11 microM, respectively. The activity of these enzymes was inhibited by EDTA. The fraction with esterase activity also displayed lipase activity, although it is unknown whether the two enzymes are identical. Variation in the activity of these esterases was examined as a function of age for normal lens and as functions of age and coloration for senile cataractous lenses. The normal lenses maintained high enzyme activity up to the 60 age group and their enzyme activity then fell abruptly. In the senile cataractous lenses, enzyme activity was very low as compared to that of normal lenses of similar age. This shows that cataract formation may have a deleterious effect on the catalytic activity of esterase in the lens.
从正常人晶状体的可溶性部分中部分纯化出两种酯酶组分。这些酶的表观分子量分别约为200 kDa（酯酶I）和30 kDa（酯酶II）。酯酶I和酯酶II的最适pH值分别为6.0和7.5，各自的最适温度分别为43℃和46℃。酯酶I和酯酶II对4-甲基伞形酮棕榈酸酯的K(m)值分别为0.14和0.11 microM。这些酶的活性受到EDTA的抑制。具有酯酶活性的组分也表现出脂肪酶活性，尽管这两种酶是否相同尚不清楚。研究了这些酯酶活性随年龄的变化情况，正常晶状体以年龄为函数，老年性白内障晶状体以年龄和颜色变化为函数。正常晶状体在60岁年龄组之前保持较高的酶活性，然后酶活性急剧下降。在老年性白内障晶状体中，与相似年龄的正常晶状体相比，酶活性非常低。这表明白内障的形成可能对晶状体中酯酶的催化活性产生有害影响。
