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Biomedical subjects

K Mertens

Publications and source records attributed to K Mertens.

78 records · Page 5Linked to original sources
PubMed1983

Activation of human prothrombin by stoichiometric levels of staphylocoagulase.

The activation of human prothrombin by the bacterial protein staphylocoagulase proceeds via the formation of a very stable equimolar complex. Unmasking of the active center in the prothrombin moiety of the complex is not caused by limited proteolysis. The kinetics of activation of human prothrombin by staphylocoagulase has been studied. The second order rate constant at pH 7.5, 37 degrees C, is 3.3 X 10(6) M-1 S-1. This reaction rate is close to reported diffusion-controlled rates of protein-protein interaction. The dissociation constant of the complex was too low to be measurable. From the kinetic data it is assumed that the first order rate constant for dissociation is orders of magnitude less than 10(-5) S-1. However, dissociation of the complex did occur in the presence of sodium dodecyl sulfate. Equimolar amounts of staphylocoagulase protect human thrombin, but not human factor Xa and bovine thrombin, against inactivation by antithrombin III. From these findings we postulate that tertiary structural changes in the thrombin region of prothrombin caused by a highly specific interaction between staphylocoagulase and that region unmask the active site.

Amino Acids↗
PubMed1982

Protein C deficiency in a Dutch family with thrombotic disease.

A rabbit antibody against human protein C was used for the quantitative estimation of protein C in plasma. In healthy individuals protein C antigen ranged from 0.65-1.45 U/ml. Plasma protein C antigen was found to be independent of either age or sex. Under influence of oral anticoagulant treatment the protein C antigen concentration decreased to 0.47 U/ml (at low intensity treatment) or 0.33 U/ml (at high intensity treatment). Using normal ranges of protein C and protein C/factor II and protein C/factor X ratios criteria were developed for the assessment of protein C deficiency. In a Dutch family with a history of thrombotic disease two members were found to have an isolated protein C deficiency, while a third one is suspected of protein C deficiency. In one case it was possible to confirm the diagnosis of suspected protein C deficiency during temporary withdrawal of the anticoagulant therapy.

Adult↗
PubMed1982

Activation of human coagulation factor VIII by activated factor X, the common product of the intrinsic and the extrinsic pathway of blood coagulation.

The intrinsic activation of human factor X has been studied in a system consisting of purified factors and in plasma. In both these systems factor Xa stimulated the activation of factor X by factor IXa plus factor VIII. This is due to the activation of factor VIII by factor Xa. When this factor Xa is formed via the extrinsic pathway, the extrinsic factor X activator functions as a stimulator of the intrinsic factor X activator.

Blood Coagulation↗
PubMed1980

Pathways in the activation of human coagulation factor X.

Purified human Factor X (apparent mol.wt. 72000), which consists of two polypeptide chains (mol.wt. 55000 and 19000), was activated by both Russell's-viper venom and the purified physiological activators (Factor VII/tissue factor and Factor IXa/Factor VIII). They all convert Factor X to catalytically active Factor Xa (mol.wt. 54000) by cleaving the heavy chain at a site on the N-terminal region. In the presence of Ca2+ and phospholipid, the Factor Xa formed catalyses (a) the cleavage of a small peptide (mol.wt. 4000) from the C-terminal region of the heavy chain of Factor Xa, resulting in a second active form (mol.wt. 50000), and (b) the cleavage of a peptide containing the active-site serine residue (mol.wt. 13000) from the C-terminal region of the heavy chain of Factor X, resulting in an inactivatable component (mol.wt. 59000). A nomenclature for the various products is proposed.

Binding Sites↗
PubMedDate not supplied

Marked species specificity of guinea pig luteinizing hormone: validation of a bioassay.

The Guinea pig is a potentially interesting alternative small animal model for the study of the neuroendocrine regulation of reproduction. However, appropriate gonadotropin assays are not widely available for this species. The aim of the present study was to validate a bioassay procedure for guinea pig luteinizing hormone (LH). The well-established interstitial cell-testosterone in vitro bioassays with the use of dispersed mouse or rat Leydig cells, successfully applied for measurement of LH from a variety of mammalian species, were found to be unsuitable for assay of guinea pig LH because of a marked species specificity of guinea pig LH. An alternative bioassay procedure was established with the use of dispersed guinea pig Leydig cells. This assay has been shown to allow for the assessment of serum LH response to exogenous gonadotropin-releasing hormone and of the expected spontaneous pulsatile pattern of basal LH secretion, with an apparent mean serum LH pulse interval of 31.4 minutes and 51.9 minutes, in long-term castrated and sham operated male guinea pigs, respectively. This bioassay can be a useful tool for more intensive exploration of guinea pig reproductive physiology.

Animals↗