Role of plasma accelerator-globulin and serum accelerator-globulin in conversion of prothrombin

Either plasma accelerator-globulin or serum accelerator-globulin must be present in order to obtain complete conversion of prothrombin in the presence of serum-eluate factor(s) [proconvertin or plasma thromboplastin component or both], antihemophilic factor, platelet factor 3, and calcium ions. If plasma accelerator-globulin is present, it must first be converted to serum accelerator-globulin by the action of thrombin before the maximum rate of prothrombin conversion is reached. Serum accelerator-globulin does neither affect the degree nor the rate of interaction of serum-eluate factor(s), antihemophilic factor, platelet factor 3, and calcium ions forming a prothrombin-conversion factor but affects thrombin formation at a point just prior to or during the conversion of prothrombin.

Cellular site for prothrombin synthesis

The cell type responsible for synthesis of any of the trace plasma proteins concerned in blood coagulation has not been identified before. In this study the fluorescent antibody technique was used to find out the cellular site for prothrombin synthesis. Fluorescent antiprothrombin precipitated out on bovine liver parenchymal cells containing adequate concentrations of prothrombin. The specificity of the reaction was established using various absorptive and blocking techniques. The antiprothrombins produced were species specific. Not all parenchymal cells reacted uniformly with fluorescent antiprothrombin so that groups of brilliantly fluorescing cells were seen among cells displaying dim natural fluorescence. This may mean that only a certain type of parenchymal cell produces prothrombin or that there is cyclic production of prothrombin.

Partial activation of prothrombin and generation of prothrombin-R with cathepsin B

Maximal yields of prothrombin-R were readily produced from a number of prothrombin derivatives when these were mixed with purified cathepsin B at pH 7.9. Thrombin was not a product when substrates prepared with either mitochondria or cathepsin B were used in the regeneration system. Conditions were found where the formation of prothrombin-R exhibited characteristics of either zero or first order kinetics with respect to the enzyme, cathepsin B. Iodoacetate partially or completely inhibited the formation of prothrombin-R. Various mechanisms which may account for the production of prothrombin-R are discussed.

PEPTIDES ATTACHED TO THROMBIN: THEIR INFLUENCE ON PROTEOLYSIS

During the activation of prothrombin at least two peptides are split off the molecule. These peptides become attached to thrombin, changing its proteolytic activity. Depending on the peptide adsorbed the endopeptidase activity of thrombin increases or diminishes. Acidification of thrombin by acetylation of amino groups uncovers the influence of peptides on the properties of thrombin.