Protein, enzyme, and isoenzyme distribution in human serum fractions obtained by ultracentrifugation.

We have described the protein, enzyme, and isoenzyme characteristics of three gross fractions of both normal and abnormal human sera, as obtained by application of high centrifugal force. In the absence of solution gradient, such fractions represent pure and undiluted elements of the serum; they are reproducible and sufficiently voluminous for extensive analytical study. Specific features of these fractions may be of interest in planning additional or peripheral investigations of serum. Fraction I appears to be a fair sample of native serum water; Fraction II appears to segregate the pre$-globulin lipoprotein component observed in some sera; Fraction III is a concentrated solution of LDH, CPK, and SGOT enzymes, and y-globulin-rich protein, which is lipoprotein-free. More than 95% of the LDH, CPK, and SGOT is located in Fractions II and III. Quantitative activity and qualitative nature of these enzymes appears to survive the stress of the ultracentrifuge technique relatively well.