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Biomedical subjects

M F Scully

Publications and source records attributed to M F Scully.

At least 19 recordsLinked to original sources
PubMed1992

Non-specific influence of chemical modification upon the properties of antithrombin III:modification of carboxyl groups.

The ability of antithrombin III to inhibit thrombin was observed to be rapidly inactivated upon specific modification of carboxyl groups. The loss of activity, upon treatment with nitrotyrosyl ester in the presence of 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide metho-p-toluenesulfonate, was concomitant to the incorporation of 2 moles of nitrotyrosine per mole of inhibitor indicating the modification of only two carboxyl groups. Moreover, the modification occurred with loss, also, of the ability of the native protein to bind tightly to heparin. The modified antithrombin III retained a reduced affinity for heparin (eluting at 0.3M NaCl from heparin Agarose) and was observed to be a competitive inhibitor of the heparin-dependent rate of inhibition of thrombin by native antithrombin III. However, FAB-MS (fast atom bombardment mass spectroscopy) analysis of digests of modified material gave no indication that modification was localized to specific Asp or Glu residues. It is concluded that the loss of activity is due to deleterious change in conformation during modification. These findings, together with our previous report upon tryptophan modification of antithrombin III [1] suggest that the nature of the molecule is such that considerable care must be taken in interpretation of results when investigating the structure/function relationships of this protein by chemical modification.

Antithrombin III↗
PubMed1992

Generation of forms of fragment E with differing thrombin-binding properties during digestion of fibrinogen by plasmin.

Two principal forms of fragment E are generated upon digestion of fibrinogen by plasmin, according to the concentration of enzyme used. At a high concentration of plasmin (above 10 micrograms/ml), a form lacking fibrinopeptide A (FpA) at the N-terminus of the A alpha-chain was generated. This form of fragment E caused a dose-dependent increase in thrombin clotting times but had no measurable inhibitory activity towards thrombin cleavage of D-phenylalanyl-L-pipecolyl-L-arginine p-nitroanilide. At a low concentration of plasmin (less than 1 microgram/ml), fragment E containing 35-40% of the original amount of FpA was present in the terminal digest. The FpA-containing form of fragment E inhibited thrombin cleavage of fibrinogen, inhibited amidolytic activity and bound to the enzyme with an affinity 3-fold tighter than fibrinogen itself (Kd 4.1 +/- 0.3 microM as opposed to 12.7 +/- 1.8 microM). During digestion of fibrinogen at low plasmin concentration, up to 65% of the FpA was cleaved just subsequent to the progressive release of B beta-(1-42)-peptide, and the Arg-16-Gly-17 bond of the A alpha-chain became relatively stable towards plasmin action when present in fragment E (and possibly fragment Y). It is proposed that both forms of fragment E can inhibit clotting by binding to the fibrin(ogen)-recognition site (anion-binding exosite) of thrombin. The FpA-containing form of fragment E can also inhibit binding that occurs distal to the P1 site and thereby interfere with amidolysis of the peptide substrate. Our finding of a lability of the Arg-16-Gly-17 bond in the early phase of digestion may provide an alternative explanation of the increased FpA concentrations observed during thrombolytic therapy.

Binding Sites↗
PubMed1991

Influence of intrinsic and extrinsic plasminogen upon the lysis of thrombi in vitro.

When the rate of lysis of artificial thrombi (prepared from plasma or whole blood) was expressed according to the concentration of tissue type plasminogen activator (t-PA) or single chain urokinase type plasminogen activator (sc-uPA) then bell-shaped dose response curves were obtained, low rates being observed at concentrations of activator greater than 500 units/ml. Bell-shaped dose response curves were not observed for rate of lysis of artificial thrombi over the concentrations of streptokinase tested (SK) or for the lysis of plasma gel clots by any of the activators tested. Further investigation indicated that the preponderant mechanism for dissolution of thrombi at 500 units/ml of t-PA was by activation of the plasminogen within the thrombus (intrinsic) since the plasminogen present in the plasma perfusing the thrombus (extrinsic) rapidly became depleted. On the other hand, at 50 units/ml t-PA the lysis was observed to be due preponderantly to the action of plasmin arising from extrinsic rather than intrinsic plasminogen. If "plasminogen enriched" thrombi were prepared in the presence of Lys plasminogen (Lys-Plg) faster rates of lysis occurred and bell-shaped biometric curves were not observed.

Fibrin↗
PubMed1977

Methods for semi micro or automated determination of thrombin, antithrombin, and heparin cofactor using he substrate, H-D-Phe-Pip-Arg-p-nitroanilide-2HCl.

Methods for the measurement of thrombin and plasma antithrombin, by end point determination at a semi micro level and also by rate assay measurement in a fully automated system have been devised using the thrombin specific chromogenic substrate, H-D-Phe-Pip-Arg-p-nitroanilide. Preliminary defibrination of plasma is avoided in both methods. The semi micro method has been correlated with antitrhombin measured in plasma of postoperative patients by established clotting and immunological assays. The automated method has been found to be highly reproducible and to have less scatter than the other procedures.

Alpha-Globulins↗
PubMed1977

Intermittent plasminogen-streptokinase treatment of deep vein thrombosis.

The fibrinolytic response of 12 patients receiving single daily infusions of 600,000 units of streptokinase (SK) and 90 mg of plasminogen for the treatment of DVT has been studied. The mean plasminogen concentration was maintained throughout the treatment period (4-6 days) at between 20-40% the initial value, while mean circulating plasmin concentration rose to only about twice initial plasma levels. The degradation of fibrinogen as indicated by a fall in clottable fibrinogen did not fall below 1 mg/ml and serum FDP rose to greater than 1 mg/ml. Limited fibrinogenolysis occurred in 2 patients, while in another patient who bled there was immediate and extensive depletion to below 0.5 mg/ml. The beneficial clinical results obtained with this regimen (Kakkar et al. 1975), which produces only limited systemic plasminaemia, suggest that thrombolysis may be facilitated by higher levels of plasminogen than those maintained during conventional SK treatment.

Fibrin Fibrinogen Degradation Products↗
PubMed1977

Acquired dysfibrinogenaemia in acute and chronic liver disease.

Plasma from patients with both acute and chronic liver disease has been examined for evidence of acquired dysfibrinogenaemia, using electrophoretic methods and coagulation tests. An examination of isolated fibrins upon SDS polyacryamide gel electrophoresis failed to demonstrate any molecular or structural defect associated with the polypeptide chains of the patients' fibrinogen or fibrinogen derivatives produced by thrombin or plasmin. However, purified fibrin monomers isolated from plasma using both Reptilase and thrombin exhibited delayed polymerization rates and the occurrence of acquired dysfibrinogenaemia in liver disease is therefore confirmed.

Acute Disease↗