gamma-A Gamma Research Articles

G gamma and A gamma globin-chain biosynthesis by adult and umbilical cord blood erythropoietic bursts and reticulocytes

We examined gamma-globin-chain biosynthesis by adult and umbilical cord blood or erythropoietic bursts in methylcellulose clonal culture and gamma-chain synthesis by cord blood reticulocytes. Globin chains were labeled with 14C-amino acids and guantitated by using autoradiography or fluorography. Alpha, beta, and G gamma and A gamma chains were separated by isoelectric focusing in polyacrylamide gels containing 8 M urea and 3% Nonidet P-40 (a nonionic detergent). Time course examinations of the gamma-chains synthesized by the bursts revealed no changes in the G gamma:A gamma ratio between days 10 and 18 of culture. The ratio of G gamma/(G gamma + A gamma) in cultures of adult circulating erythroid precursors was 0.38 +/- 0.09, which corresponds to the known ratio in adult peripheral blood erythrocytes. The relative G gamma-chain biosyntheses in the cord blood bursts and reticulocytes were 0.56 +/- 0.02 and 0.66 +/- .008, respectively. Both are intermediate between the accepted newborn and adult ratios. Natal erythropoietic precursors appear to be in the transitional stage with respect to the switching of G gamma-A gamma ratios.

Demonstration of a large molecular weight variant of the gamma chain of normal human plasma fibrinogen.

A previously undescribed gamma chain variant of human fibrinogen has been identified by application of a sensitive sodium dodecyl sulfate-polyacrylamide gradient gel electrophoretic technique to separate the polypeptide chains. This variant, called gamma B, clots and cross-links as well as the major species (gamma A), is similarly degraded by plasmin, and has a molecular weight of 53,100 as compared to 50,100 for gamma A. Cross-linked dimers of Mr = 100,100 and 108,500 are identified after action of thrombin and Factor XIIIa, suggesting the formation of gamma A-gamma A and gamma B-gamma B dimers rather than gamma A-gamma B hybrid species. The gamma B chain dimers represent 16% of the total cross-linked gamma chain forms. Two early plasmic derivatives of gamma A and gamma B chains have been demonstrated to have lost fragments of Mr = approximately 4,000 and 5,000 without loss of 5-dimethylaminonaphthalene-1-sulfonyl cadaverine fluorescence. Since the difference in molecular weight of gamma A and gamma B chains is maintained during plasmic degradation of both monomer and dimeric fluorescent forms, this suggests that the additional sequence of amino acids in gamma B is located at or near the COOH-terminal end of this polypeptide chain.