John R. Carter

Bio: John R. Carter is an academic researcher. The author has contributed to research in topics: Prothrombinase & Moiety. The author has an hindex of 3, co-authored 3 publications receiving 39 citations.

Concept of a common protein moiety, containing disulfide bonds, in prothrombin, prothrombin derivative (autoprothrombin) and thrombin.

Abstract: With a recently devised argentometric amperometric method, disulfide was demonstrated in biothrombin, citrate thrombin and prothrombin derivative (autoprothrombin) in the same quantity (43 µm/100 m...

The Fibrinogen-Fibrin Conversion1

Abstract: Publisher Summary The thrombin-induced conversion of fibrinogen to fibrin that is the primary subject of this review is essentially the final stage in the complex series of processes involved in blood coagulation. Fibrinogen exists in normal blood, while thrombin is present as its precursor prothrombin. The coagulation process consists of the conversion of prothrombin to thrombin and of the subsequent action of thrombin on fibrinogen to produce fibrin. In the fibrinogen-fibrin conversion fibrinogen, already a high polymer of many amino acids is converted to an even higher polymeric form or coagulum, the fibrin clot. Prothrombin can be converted to thrombin in a series of highly complex, and as yet not well understood, reactions. The chapter explores four of the processes by which the conversion of prothrombin to thrombin takes place. These are (1) activation by citrate, (2) activation by calcium ions, Ac-globulin and thromboplastin, (3) activation by calcium ions, platelets and thromboplastin, and (4) activation by trypsin. The chapter concludes by addressing the various problems of current interest in protein chemistry, which appear in the study of the fibrinogen-fibrin conversion. The first step is an example of a limited proteolysis by a protease of curious specificity. This proteolysis may turn out to be one of the first illustrations of the existence of “strong” peptide bonds in proteins. Further, it offers a nice illustration of the phenomenon of unmasking or activation in biological systems. The second step involves protein-protein associations with unequal association constants. The last step may involve gel formation or crystallization.

Some properties of an esterase derived from preparations of the first component of complement.

Abstract: Studies on an esterase derived from partially purified preparations of the first component of complement are described. The esterase hydrolyzed certain synthetic amino acid esters, among which N-acetyl-L-tyrosine ethyl ester was most susceptible. This was hydrolyzed maximally between pH 7.5 and 8.2, and at 41°C. The esterase could not be identified with other previously described hydrolytic enzymes. An esterase with similar properties could also be eluted from antigen-antibody aggregates which had been treated with serum. Human serum contained a heat-labile inhibitor of the esterase which could not be identified with any of the known components of complement. The esterase was also inhibited by certain reducing agents. The experiments described support the early hypothesis that complement exerts its action enzymatically, but the physiological role of the esterase derived from preparations of complement is not yet clear.

9 Thrombin and Prothrombin

Abstract: Publisher Summary This chapter focuses on the molecular and catalytic properties of thrombin and prothrombin. Prothrombin and thrombin as well as fibrinogen have been found in blood plasma in all classes of vertebrates. The chapter describes the specific assay methods that measure the fibrinogen-clotting activity of thrombin. This clotting involves both limited proteolysis of fibrinogen and the polymerization process that follows. Thrombin catalyzes only the proteolysis. An assay that depends only on this proteolytic step has been developed. It measures the increase in N-terminal glycine as the fibrinopeptidyl-fibrin monomer bonds in fibrinogen are split by thrombin. Assays based on the esterase activity of thrombin, particularly against arginyl and lysyl substrates with a blocked α-amino group, have also been developed. Two types of clotting assay have been used for prothrombin. In the one-stage method, the activation of prothrombin to thrombin, proteolysis of fibrinogen by thrombin, and polymerization of fibrin monomer to form a visible clot, all occur in the same reaction mixture. In the two-stage assay, the activation of prothrombin takes place in a separate mixture from which samples are assayed for thrombin activity as a function of activation time.

Fibrinogen to Fibrin Transformation

Abstract: So each man strives to flee that secret foe Which is himself. But move he swift or slow, That self, for ever punctual at his heels, Never for one short hour will let him go.