SummaryHuman fibrinogen was isolated from the blood of adults and from umbilical cord blood. The fibrinogen preparations obtained were clottable with thrombin to between 97 and 98% and homogeneous in acrylamide gel electrophoresis. Comparative analyses of these highly purified foetal and adult fibrinogen showed that they have the same quantitative amino acid composition and the same mobility in acrylamide gel electrophoresis at pH 9.2.Chromatography on DEAE-cellulose made it likely that foetal and adult fibrinogen have a slightly different electrical charge. The pH-dependency of the thrombin clotting time is strikingly different. The fingerprints of the tryptic peptides showed at least 3 peptides with different mobility in chromatography.From these data it is assumed that foetal and adult fibrinogen have a different molecular structure. Hitherto it cannot be decided if the two proteins have a different primary structure, which is most probable, or if they are chemical modifications.
Antithrombin III (AT III) levels are markedly increased in newborn infants following exchange transfusion with adult blood, and subsequently return to pre-exchange values. This transient rise in AT III (heparin cofactor activity), was used to estimate its plasma elimination half-life. AT III activities were measured serially, before and after double-volume exchange transfusions with heparinised blood in newborn infants requiring therapy for severe hyperbilirubinaemia. The plasma elimination half-life of AT III activity was calculated to be 3.9 +/- 1.4 h (mean +/- SEM). Compared with published data on the kinetics of AT III infusions in adults, the neonate has a considerably accelerated turnover. This finding has important implications for the design of future therapeutic trials of AT III concentrates and provides further evidence that plasma proteins, including components of the coagulation system, appear to have different kinetics in the neonatal period.
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