Biomedical subjects

R Procyk

Publications and source records attributed to R Procyk.

23 records · Page 2Linked to original sources

PubMed1987

Alternative pathways in blood coagulation.

Two thrombin independent reactions involving polymerization and gelation of fibrinogen (FBG) and of FBG and fibronectin (FN) are described. In the first reaction FXIII, in the presence of calcium ions, induces oligomerization and eventually complete gelation of FBG, i.e. formation of fibrinogenin. FBG dimers and probably also higher oligomers are formed by the crosslinking of gamma-chains prior to gelation. During gelation the A alpha-chains also become completely crosslinked. These reactions are enhanced by a variety of thiol compounds. With DTT, reduction of specific disulfides in the A alpha-chain of FBG appear to be responsible for the enhancement. In the second reaction, FXII catalyzes the formation of heteropolymers of FBG-FN. These complexes eventually form visible particulate matter called heteronectin. Dimers consisting of 1 mole FBG and 1 mole FN form first, followed by the appearance of higher order heteronectin intermediates. In heteronectin the A alpha-chain of FBG provides the linkage to FN. Thiols also enhance the heteronectin reaction. Formation of fibrinogen and/or heteronectin depends upon the initial relative concentrations of FBG and FN. At equimolar concentrations mainly heteronectin is formed. During clotting of normal whole blood, thrombin induced fibrin formation is the initial event followed by rapid fibrinogen formation. Addition of iodoacetamide (an inhibitor of FXIII) to whole blood prevents the formation of fibrinogenin. These findings suggest that the fibrinogen pathway is important in vivo.

Blood Coagulation↗

PubMed1985

Factor XIII catalyzed formation of fibrinogen-fibronectin oligomers--a thiol enhanced process.

Fibrinogen and plasma fibronectin were shown to interact in the presence of factor XIIIa. The reaction was enhanced by dithiothreitol and was accompanied by an increase in the turbidity of the solution and the formation of particulate matter and gel structures. At a constant concentration of fibrinogen the turbidity increase was dependent on the fibronectin concentration and at a constant concentration of fibronectin, on the fibrinogen concentration. Kinetic experiments showed that an initial step in the reaction between fibrinogen and fibronectin was the formation of a transient intermediate containing 1 mole of fibrinogen and 1 mole of fibronectin. Transient intermediates of larger molecular weight and containing both fibrinogen and fibronectin were also formed. These heterooligomers eventually reached huge molecular sizes and at early times formed particulate matter that sedimented on centrifugation. The predominant molecular species formed in an equimolar mixture of fibrinogen and fibronectin were heteropolymers. Small amounts of homopolymers composed of fibrinogen and possibly also homopolymers of fibronectin were detected. The results are discussed in terms of reaction mechanism and potential importance of this novel oligomerization pathway in haemostasis, thrombosis and tissue repair.

Dithiothreitol↗

PubMed1985

FXIII induced gelation of human fibrinogen--an alternative thiol enhanced, thrombin independent pathway.

Factor XIII induced gelation of human fibrinogen in the presence of calcium ions. At the end of this reaction between 95 and 100% of the fibrinogen was incorporated into the gel matrix. The gelation was dramatically enhanced by DTT. Cysteine and beta-mercaptoethanol also enhanced the reaction, but less efficiently. Thrombin activated factor XIII led to shortened gelation time and increased the rate of gelation. The reaction was inhibited by p-chloromercuribenzoate and iodoacetamide. Neither fibrinopeptide A, nor fibrinopeptide B were released during gelation, while quantitative release of FPA by thrombin was demonstrated from preformed gel matrices. SDS-PAGE showed the presence of gamma-dimers and alpha-polymers in the gel matrix. In the clot supernatants gamma-dimers were observed already before the gel point. We also observed that the clotting of fibrinogen by thrombin was perturbed by DTT. Preincubation of fibrinogen with calcium ions prevented this effect of DTT.

Calcium↗

PubMed1979

Cycloheximide as a probe of fibrinogen synthesis.

Fibrinogen synthesis in the intact rat was perturbed by treatment with cycloheximide. Specific radioactivities of fibrinogen in plasma and liver both decreased at 2 h after treatment and increased over 2-fold by 18 h. Labelled-antibody--polyribosome binding experiments showed that more polyribosomes were engaged in fibrinogen synthesis at 18 h after treatment. Radioactivity of plasma fibrinogen chains from untreated control rats showed a constant ratio of A alpha--B beta/gamma = 1.03. At 2 h after cycloheximide treatment the A alpha- and B beta-chains showed the greatest decrease in labelling (A alpha--B beta/gamma = 0.66) and at 18 h all chains were much more labelled (the A alpha--B beta/gamma ratio chainged to 1.39). The observed imbalance in fibrinogen-chain synthesis suggests that cycloheximide has a selective effect on gene expression.

Animals↗

PubMed1977

Regulation of mammalian protein synthesis in vivo. Stimulated protein synthesis in liver in vivo after cycloheximide treatment.

Protein synthesis in rat liver in vivo was measured between 0 and 72 h after administration of a non-lethal dose of cycloheximide. There was a period of inhibition of [3H]leucine incorporation into both intra- and extra-cellular proteins at 2 h after administration of the drug, which was followed by a recovery phase in which amino acid incorporation varied significantly among the various proteins evaluated. At 12 h there was a marked stimulation of incorporation into nascent polypeptides released from polyribosomes and plasma fibrinogen, but incorporation into ribosomal proteins as well as albumin was still inhibited. Between 12 and 48 h, nascent-polypeptide synthesis remained elevated, but ribosomal-protein synthesis recovered slowly from the inhibition to normal rates only, and plasma-albumin synthesis increased slowly to above control values up to 48 h before returning to normal. A differential pattern of incorporation was also observed for incorporation into free and membrane-bound polyribosomes.

Animals↗