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Biomedical subjects

M J Griffith

Publications and source records attributed to M J Griffith.

At least 91 records · Page 5Linked to original sources
PubMed1984

Awareness by consumers and the adoption of a new service: an HMO example.

Researchers and managers of health care organizations must take two fundamental issues into account when examining the process by which consumers decide to use a new service. First, one cannot assume that if one member of a family uses the service, everyone in the family does. Historically, these points have not been given sufficient heed in the design of adoption studies. By using HMO enrollment as an example, the authors show the problems that could result from the above assumptions.

Awareness↗
PubMed1984

Start-up analysis for marketing strategy.

The complex start-up effect on utilization of health care services is too often overlooked or underestimated by marketing planners, leading to a range of negative consequences for both the users of services and the provider organization. Start-up analysis allows accurate estimation of these utilization effects for coordinated strategic planning among marketing finance, and operations.

Health Maintenance Organizations↗
PubMed1984

Policy implications of startup utilization by enrollees in prepaid group plans.

This article discusses several policy implications of the so-called startup effect, in which high initial health services utilization by new enrollees in prepaid group plans ( PGPs ) becomes reduced with the increasing duration of membership. Results of research in a developing PGP are analyzed as they relate to a mathematical model of startups for two measures of enrollee use. After estimating the total costs of startups in this setting, the motivating effects of such costs on PGPs are examined in relation to several policy issues--including the rate of PGP development in the United States, the use of financial incentives to enroll the elderly and medically disadvantaged, potential inequities of premium determination, the large impact of startups on disenrollment , and the federally mandated process of annual announcement of benefits and open enrollment. Ideas and mechanisms for future study on the startup effect and its policy implications are discussed.

Costs and Cost Analysis↗
PubMed1983

Dermatan sulfate and heparin can be fractionated by affinity for heparin cofactor II.

Commercial preparations of dermatan sulfate and heparin were applied to a concanavalin A-agarose to which heparin cofactor II had been noncovalently bound. Small amounts of both mucopolysaccharides bound to the column with relatively high affinity. Heparin and dermatan sulfate which were eluted from the affinity column catalyzed the inhibition of thrombin by heparin cofactor II to a greater degree than did the respective unfractionated mucopolysaccharides. Dermatan sulfate did not catalyze thrombin inhibition by antithrombin III. The results suggest that heparin cofactor II differs from antithrombin III with respect to the mucopolysaccharide binding site.

Catalysis↗
PubMed1983

Calcium inhibits the heparin-catalyzed antithrombin III/thrombin reaction by decreasing the apparent binding affinity of heparin for thrombin.

The present study has shown that calcium inhibits the heparin-catalyzed antithrombin III/thrombin reaction. The initial rate of thrombin (4.0 nM) inhibition by antithrombin III (200 nM) in the presence of heparin (2.5 ng/ml) decreased from 3.6 nM/min (in the absence of calcium) to 0.12 nM/min in the presence of 10 mM calcium. In the absence of heparin, the initial rate of thrombin inhibition by antithrombin III was not affected by calcium. The heparin-catalyzed antithrombin III/thrombin reaction is described by the general rate equation for a random-order, bireactant, enzyme-catalyzed reaction (M. J. Griffith (1982) J. Biol. Chem. 257, 13899-13902). As such, the reaction is saturable with respect to both thrombin and antithrombin III. The apparent kinetic parameters for the heparin-catalyzed antithrombin III/thrombin reaction were determined in the presence and absence of calcium. The apparent heparin/antithrombin III dissociation constant values were not measurably different in the presence of 0, 1.0, and 3.0 mM calcium. The apparent heparin/thrombin dissociation constant value increased from 7.0 nM, in the absence of calcium, to 10 and 30 nM in the presence of 1.0 and 3.0 mM calcium, respectively. The maximum reaction velocity, at saturation with respect to both proteins, was not affected by calcium. It is concluded that calcium binds to functional groups within the heparin molecule which are required for thrombin binding.

Animals↗
PubMed1983

Identification of the molecular defect in factor IX Chapel Hill: substitution of histidine for arginine at position 145.

Hemophilia B Chapel Hill is a mild hereditary hemorrhagic disorder in which the factor IX antigen is present in normal amounts but factor IX biological activity is markedly reduced. Previous studies have demonstrated that purified factor IX Chapel Hill has 8% of the activity of normal human factor IX and that the activation of factor IX Chapel Hill is defective in that only one of the two peptide bonds hydrolyzed during activation of normal factor IX is cleaved. The tryptic peptides from normal human factor IX and factor IX Chapel Hill were subjected to analysis by high-performance liquid chromatography. Comparison of the elution profile of the peptides obtained from factor IX Chapel Hill and normal factor IX demonstrated that the tripeptide Leu-Thr-Arg, which is derived from the normal molecule (positions 143-145) immediately amino-terminal from the Arg-Ala peptide bond at 145-146 that is cleaved during the activation of factor IX with factor XIa, was absent in the digest obtained from factor factor IX Chapel Hill. The elongated "activation peptide" from factor factor IX Chapel Hill was obtained by further high-performance liquid chromatographic fractionation and subjected to primary structure analysis. The following sequence, corresponding to positions 143-147, was obtained: Leu-Thr-His-Ala-Glu. Thus, the primary molecular defect in factor factor IX Chapel Hill is the substitution of histidine for arginine at position 145. This substitution precludes cleavage by factor XIa at this peptide bond, and the activation peptide region remains associated with the light chain of factor IXa Chapel Hill.

Amino Acid Sequence↗
PubMed1983

Heparin-catalyzed inhibitor/protease reactions: kinetic evidence for a common mechanism of action of heparin.

Three different heparin-catalyzed inhibitor/protease reactions were studied: antithrombin III/thrombin, heparin cofactor II/thrombin, antithrombin III/factor Xa. The three reactions were saturable with respect to both inhibitor and protease. The initial reaction velocity, for each reaction, could be described by the general rate equation for a random-order bireactant enzyme-catalyzed reaction. The kinetic parameters for the heparin-catalyzed antithrombin III/thrombin and antithrombin III/factor Xa reactions differed in terms of apparent maximum velocity (Vmax) and apparent heparin-protease dissociation constant values. The apparent heparin-antithrombin III dissociation constant values were the same for both reactions. The kinetic parameters for the heparin-catalyzed antithrombin III/thrombin and heparin cofactor II/thrombin reactions differed in terms of apparent Vmax and apparent heparin-inhibitor dissociation constant values. The apparent heparin-thrombin dissociation constant values were the same for both reactions. The results are consistent with a general mechanism of action of heparin for the three reactions that, in its simplest form, requires only that both protease and inhibitor bind to heparin for catalysis to occur.

Antithrombin III↗
PubMed1983

Structure-activity relationships of heparin. Independence of heparin charge density and antithrombin-binding domains in thrombin inhibition by antithrombin and heparin cofactor II.

To better understand how heparin structure affects its activity the relationships between the functional domains for inhibitor binding and charge density were investigated to determine how these domains affect heparin-mediated thrombin inhibition by two different heparin-dependent protease inhibitors, antithrombin (AT) and heparin cofactor II (HC II). A series of heparins, fractionated systematically by charge density, was further fractionated on antithrombin agarose to isolate more homogeneous subfractions that were either inactive or highly active with respect to thrombin inhibition by AT. With AT, the activities of the AT-active subfractions increased sharply with heparin charge density, while those with little or no affinity for AT were virtually inactive. In contrast, with HC II inhibitor, the activities of the heparins depended only upon their charge densities and were independent of AT affinity. At any given charge density, the heparin before fractionation by AT affinity and the fractions that were highly active and inactive with AT were all equally active with HC II. The two inhibitors also differed in their reactivity with heparan sulfate and dermatan sulfate. A charge-density effect with the subfractions having similar high affinity for AT demonstrates that charge density represents a heparin functional domain that is independent of the AT-binding domain. The behavior of the AT-inactive heparins, being fully active with HC II, demonstrates the functional domain necessary for AT binding is not needed to produce HC II activity.

Animals↗
PubMed1983

Heparin cofactor activities in a family with hereditary antithrombin III deficiency: evidence for a second heparin cofactor in human plasma.

Plasma levels of antithrombin-heparin cofactor, determined by heparin-dependent antithrombin assay, and antithrombin III antigen were measured in 22 members of a large kindred predisposed to venous thrombosis. While 11 members had reduced plasma levels of both antithrombin-heparin cofactor and antithrombin III antigen, the levels of antithrombin-heparin cofactor were always greater than the levels of antithrombin III antigen: 66% (+/- 7%) and 49% (+/- 5%) of normal plasma, respectively. Pooled normal plasma and plasma from one of the affected family members (60% antithrombin-heparin cofactor and 47% antithrombin III antigen) were fractionated by heparin-agarose affinity chromatography. Antithrombin-heparin cofactor, which eluted from heparin-agarose with buffer containing 0.4 M NaCl and did not cross-react with antibody specific for antithrombin III and did not inhibit factor Xa at an appreciable rate in the presence of heparin, was designated heparin cofactor A. Antithrombin-heparin cofactor, which eluted from heparin-agarose with buffer containing 2.0 M NaCl, was functionally and antigenically identified as antithrombin III. The concentrations of heparin cofactor A in normal and patient plasma were similar (4.5 x 10(-7) M), while the concentration of antithrombin III in patient plasma (8.0 x 10(-7) M) was only 50% of normal (1.6 x 10(-6) M). The functional properties of both heparin cofactor A and antithrombin III obtained from patient plasma were normal. From the results of the present study it would appear that the antithrombin-heparin cofactor concentrating measured in patient plasma reflects the combined concentrations of heparin cofactor A and antithrombin III. Since heparin cofactor A does not cross-react with antibody to antithrombin III, the concentration of antithrombin III antigen in patient plasma is thus lower than the concentration of antithrombin-heparin cofactor.

Antithrombin III↗
PubMed1982

The heparin-enhanced antithrombin III/thrombin reaction is saturable with respect to both thrombin and antithrombin III.

The heparin-enhanced antithrombin III/thrombin reaction was studied under experimental conditions where the dependence of the reaction velocity on the concentrations of thrombin and antithrombin III could be determined. The results have shown that the reaction is saturable with respect to both thrombin (KT = 3.6 x 10(-8) M) and antithrombin III (KAT = 1.0 x 10(-7) M) when the heparin concentration is low relative to the initial protein concentrations. The apparent first order rate constant for the rate-limiting step in the reaction was approximately 800 min-1. The reaction was subject to inhibition by antithrombin III/thrombin, the product of the reaction. Inhibition appeared to be noncompetitive with respect to antithrombin II with KP, the apparent heparin product dissociation constant, approximately equal to KT. When the heparin-enhanced antithrombin III/thrombin reaction was studied under conditions where the heparin concentration was high relative to the initial protein concentrations the overall reaction was second order. The initial reaction velocity, under any set of experimental conditions, could be described by the general rate equation for a random order bireactant, enzyme-catalyzed reaction, which is mathematically identical with the "template" model for the mechanism of action of heparin (Griffith, M. J. (1982) J. Biol. Chem. 257, 7360-7365).

Antithrombin III↗
PubMed1982

Cleavage and activation of human prothrombin by Echis carinatus venom.

The cleavage of human prothrombin by partially purified Echis carinatus venom (ECV) was investigated in the present report. Incubation of prothrombin with ECV resulted in the rapid cleavage of prothrombin to alpha-thrombin, with the release of fragment-1 and fragment-2. When dansyl arginine-N-(3-ethyl-1,5-pentanediyl) amide (DAPA), a very effective inhibitor of thrombin, was included in the ECV-prothrombin solution, meizothrombin was rapidly formed. Only small amounts of meizothrombin-1 could be detected. Prolonged incubation (23 h) in the presence of DAPA, however, resulted in nearly quantitative conversion of meizothrombin to meizothrombin-1 and fragment-1. Kinetic studies strongly suggested that the conversion of meizothrombin to meizothrombin-1 was due to ECV and not meizothrombin autolysis. In addition, EDTA, which inhibits ECV, blocked the cleavage of meizothrombin. Amino terminal sequence analysis indicated that ECV cleaves human prothrombin at two sites; Gly158-Ser159 and Arg322-Ile323. The former site differs from the site of autolytic cleavage of meizothrombin which occurs at Arg155-Ser156. In contrast to reports in the literature, the results of the present study indicate that the release of fragment-1 does not precede activation of human prothrombin by ECV.

Amino Acid Sequence↗
PubMed1982

Measurement of human factor IXa activity in an isolated factor X activation system.

To determine the functional properties of factor IX isolated from the plasma of CRM+ hemophilia B patients, an assay system using proteins isolated from human plasma had to be developed which would be amenable to kinetic studies under a variety of experimental conditions. The present study describes the activation of factor X by factor IXa, isolated from normal human plasma, in an assay system which allows manipulation of calcium, phospholipid and factor VIIIa concentrations. Initial rate measurements with factor VIIIa present in the system were made by incubating factor VIII with factor Xa immediately before factor IXa assay. With this approach, the initial rate of factor X activation was constant, with little evidence for a lag period. Within the framework of the assay system described in the present study, it should be possible to examine not only genetic variants of factor IX, but also variants of factor VIII, as well as providing a means of routine factor IXa and factor VIII(a) assays.

Blood Coagulation Tests↗
PubMed1982

Measurement of the heparin enhanced-antithrombin III/thrombin reaction rate in the presence of synthetic substrate.

An assay approach, designed to allow accurate measurement of the rate of thrombin inhibition by antithrombin III in the presence of heparin, is described. In essence the approach takes advantage of the fact that synthetic substrates, e.g. N-alpha-p-tosyl-L-glycyl-L-prolyl-L-arginine-p-nitroanilide, bind to the active site of thrombin, which slows the rate of reaction with antithrombin III. The rate of thrombin inhibition can be monitored continuously by change in absorbance at 400 nm or measured by end point determination. In either case, reproducible rate measurements can be made under a variety of experimental conditions not easily examined with conventional assay approaches.

Antithrombin III↗
PubMed1981

Structure-function relations in platelet-thrombin reactions. Inhibition of platelet-thrombin interactions by lysine modification.

The chemical modification of lysine residues in human alpha-thrombin has been used to study the interaction of thrombin with human platelets. Phosphopyridoxylation of thrombin using pyridoxal 5'-phosphate (pyridoxal-P) has been shown to inhibit the fibrinogen clotting activity of thrombin but not the catalytic activity (Griffith, M. J. J. Biol. Chem. 254, 3401-3406). Phosphopyridoxylation resulted in marked inhibition of the platelet-activating activity of thrombin. The concentration of pyridoxal-P-thrombin required to induce half-maximal platelet aggregation and release was 60 times greater than that of unmodified thrombin. Binding studies using pyridoxal-P-125I-thrombin showed a loss of both high and low affinity binding of thrombin to the surface of intact gel filtered platelets. In contrast, thrombin modified with pyridoxal-P in the presence of heparin incorporated up to 1 mol of pyridoxal-P per mol of thrombin. The heparin-protected pyridoxal-P-thrombin was only slightly inhibited in its interaction with platelets, and binding studies with the heparin-protected pyridoxal-P-125I-thrombin showed selective loss of low affinity binding but preservation of high affinity binding. These results provide further support for the hypothesis that residues at the macromolecular binding site of thrombin are involved in the binding of thrombin to platelets and further separate this functional region of thrombin into two lysine-containing subregions, one which is protected from modification by heparin which is involved in high affinity binding, and another which is not protected by heparin which is involved in low affinity binding.

Blood Platelets↗
PubMed1981

Affinity labeling of the active site of Escherichia coli glutamine synthetase by 5'-p-fluorosulfonylbenzoyladenosine.

The interaction of Escherichia coli glutamine synthetase with the adenosine 5'-triphosphate analogue, 5'-p-fluorosulfonylbenzoyladenosine (5'-FSO2BzAdo), has been studied. This interaction results in the covalent attachment of the 5'-FSO2BzAdo to the enzyme with concomitant loss of catalytic activity. Although adenine nucleotides interact with glutamine synthetase at three distinct sites--a noncovalent AMP effector site, a regulatory site of covalent adenylylation, and the catalytic ATP/ADP binding site--our studies suggest that reaction with 5'-FSO2BzAdo occurs only at the active center. When glutamine synthetase was incubated with 5'-FSO2BzAdo, the decrease in catalytic activity obeyed pseudo-first order kinetics. The plot of the observed rate constant of inactivation versus the concentration of 5'-FSO2BzAdo was hyperbolic, consistent with reversible binding of the analogue to the enzyme prior to covalent attachment. Protection against inactivation was afforded by ATP and ADP; L-glutamate did not protect the enzyme against inactivation, but rather enhanced the rate of inactivation, consistent with the observations of others (Timmons, R. B., Rhee, S. G., Luterman, D. L., and Chock, P. B. (1974) Biochemistry 13, 4479-4485) that there is synergism in the binding of the two substrates to the enzyme. The incorporation of approximately 1.09 mol of the 5'-FSO2BzAdo/mol of glutamine synthetase subunit resulted in the total loss of enzymatic activity. The results suggest that 5'-FSO2BzAdo occupies the ATP binding site at the active center of glutamine synthetase and binds covalently to an amino acid residue nearby.

Adenosine↗