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MORRIS GREEN, ROBERT S. SCHWARTZ; The Catabolism of I-131-Insulin by Rat Lens Homogenates. Invest. Ophthalmol. Vis. Sci. 1963;2(6):635-640.
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The ability of a rat lens honiogenate to degrade radioiodinated zinc insulin into fractions which now are TCA soluble was used as a criterion of proteolysis. The assay method is extremely simple, rapid, and sensitive. Proteolytic activity is linearly related to the amount of lens homogenate added. The lens enzyme has a pH optimum of approximately 7.2, a temperature maximum near 50° C, and is inactivated by sulfhydryl inhibitors and heavy metals. Almost all of the enzyme activity is found in the water soluble fraction of the lens. Addition of crystalline zinc insulin competitively inhibits the breakdoion of the I-131-insulin. This enzyme system or another enzyme exhibits a pH optimum above pH 10, a temperature maximum near 50° C, and has rather unique reaction kinetics.
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