Properties of Partially Purified Esterase in Human Crystalline Lens and Variation in Its Enzyme Activity during Aging and with Advance of Senile Cataract

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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°C and 46°C. The K_m values of esterase-I and esterase-II for 4-methylumbelliferyl-palmitate were 0.14 and 0.11 μM, 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 idnetical.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.