Enzyme Studies on Human Blood. I. Proteolytic Activity Associated with a Fraction of Plasma.

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Abstract
Studies were made on the action of whole dried plasma and its primary fractions, separated by low temp.-ethanol procedure, on casein. A test mixture consisted of 2% aq. solns. of plasma or its fractions and 2% suspension of "C.P." casein in 1/15 M Sorensen phosphate buffer of specified pH. With each test, a substrate and an enzyme control were run simultaneously. Toluene was added and frequent smears and cultures were taken. After 48 hrs. incubation at 37.5[degree]C, acid soluble total nitrogen or "tyrosine" detns. were made. No kinase was added and there was no previous treatment of the protein prepns. with chloroform or any other agents in any of the expts. Human plasma Fraction I (Cohn) contains a high degree of proteolytic activity. The enzyme is inactivated at 80[degree]C, and functions at near neutrality.