Age-related and distributional changes in the trypsin inhibitor activity of bovine lens

Age-related changes in the bovine lens trypsin inhibitor activity were measured by assaying water soluble extracts of 10 concentric slices from the periphery to the center of the lens. Inhibitor assays were carried out at pH 7.0 and 7.9 using prenatal, calf and mature lenses. The inhibitor at pH 7.0 remained constant throughout the lens but the pH 7.9 activity decreased sharply in the lens nucleus. This was particularly true for the prenatal and calf lenses. Agarose A-15 m gel filtration of the water soluble inhibitor activity showed a decrease in inhibitor in the alpha-crystallin region and a corresponding increase in inhibitor activity in the HMW protein peak. Inhibitor assays were carried out on the water insoluble fractions following solubilization in 6.0 M-urea. Little or no inhibitor activity was seen in the outer cortical fractions but the inner cortex and nucleus contained high levels of inhibitor activity in the water insoluble fraction with specific activities 7- to 10-fold higher than the comparable crude lens extracts. These data suggest that the lens inhibitor activity at pH 7.0 and 7.9 aggregate into a HMW complex and with time preferentially enter the water insoluble fraction. The distribution of a purified 5.5 K inhibitor protein between the water soluble and the water insoluble fraction was measured. In the periphery all of this inhibitor was in the water soluble fraction, but toward the center of the lens this inhibitor began shifting to the water insoluble fraction. Slices taken from the lens nuclear region showed that all the inhibitor was in the water insoluble fraction as detected by both activity measurements and SDS-PAGE.