Metabolic heterogeneity of human γ-globulin

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Abstract
I131-Labelled gamma-globulin prepared by zone electrophoresis is metabolically heterogeneous; the fractional turnover rate falls progressively in healthy human subjects during the first 7-13 days after injection. Such gamma-globulin preparations contain macroglobulin (S20 w 19) and after the labelling about 9% of the I131 is attached to this fraction. Three subtractions of gamma-globulin of increasing electrophoretic mobility and hexosamine content, but having similar sedimentation coefficients (S20 w 6.10-6.62), were prepared by anion-exchange chromatography. These fractions, which comprised about 90% of the total gamma-globulin, were metabolically homogeneous and all were identical in distribution and turnover in healthy subjects. Four different analytical methods gave similar turnover data for the chromatographic gamma-globulin fractions. The half-life was 21-26 days (mean 23 days), the extra- to intra-vascular mass ratio of gamma-globulin was 0.6-1.1 (mean 1.0) and the exchange rate between intra- and extra-vascular pools was equivalent to 19-33% (mean 25%) of the circulating gamma-globulin/day. The fractional turnover rate (% of intravascular pool/day) in normal subjects was 4.0-6.8% (mean 5.4%) and the absolute turnover rate was 1.5-2.5 g/day (mean 2.1 g/day). Gamma-macroglobulin was chromatographically distinct from the bulk of gamma-globulin; its turnover rate was more rapid and it did not equilibrate with an extravascular pool. These findings indicate that gamma-globulin prepared by electrophoresis consists of two metabolically distinct groups of molecules which differ in regard to turnover rate and distribution between extra- and intra-vascular pools.