PubMed Health⌕ Search

Biomedical subjects

G Kaldor

Publications and source records attributed to G Kaldor.

At least 19 recordsLinked to original sources
PubMed1992

Spectrophotometric and kinetic studies on normal and thyrotoxic cardiac myosins.

Kinetic and microcalorimetric methods were used to study the interaction of thyrotoxic (V1) and normal adult cardiac myosin (V3) with ATP. It was shown that the overall enthalpy and entropy change was larger in the interaction of ATP with the thyrotoxic than with the normal myosin. There is evidence that the observed enthalpy changes were generated by protein conformational changes connected to the sequential destabilization and restabilization of the prevalent, energetically favored conformation of the myosin molecule. The V1-ATP interaction created more entropy than the V3-ATP interaction, and also the thyrotoxic isomyosin required more activation energy than the normal protein to attain the activated state. All of these results indicated that the catalytic activity of the V1 myosin was thermodynamically less efficient than that of the V3 isoenzyme.

Aging↗
PubMed1990

Microcalorimetric studies of the interaction of normal and thyrotoxic cardiac myosins with ATP and ADP.

The heat production of the interaction of normal and thyrotoxic cardiac myosins with ATP and ADP was studied in a microcalorimeter. As compared to the normal protein the thyrotoxic cardiac myosin gave a larger negative enthalpy, entropy, and heat capacity change. These results indicate that the enthalpy, entropy, and heat capacity differences between the two conformational states of myosin are larger in the thyrotoxic cardiac muscle than in the normal control. The ATP induced transition between the conformational states of the cardiac myosins appears to be connected to the powerstroke of the contractile cycle. Therefore the observed thermodynamic differences between the normal and thyrotoxic cardiac myosins may be related to the active site chemistries of these isomyosins and portend the functional abnormality of the thyrotoxic cardiac muscle.

Adenosine Diphosphate↗
PubMed1988

An automated approach to characterize, in simple kinetic terms, the generation and inactivation of thrombin and the interaction of fibrinogen with thrombin.

Here, we used a fully automated, computer-directed centrifugal analyzer (which permitted simultaneous turbidimetry and calculation of results) and purified thrombin, fibrinogen, and various inhibitors to study clot formation. The Km and Vm for these reactions were useful in detecting and partly characterizing anticoagulants. We also explored the generation and inactivation of thrombin, using the two-stage prothrombin time and antithrombin activity tests. The amount of thrombin instantaneously generated and inactivated was monitored under artificially created pathological conditions. The pseudo-first-order rate constant for thrombin generation and inactivation and the instantaneous concentration of enzymatically active and inactive thrombin were used in the characterization of these conditions. We believe this approach is suitable for routine clinical use.

Algorithms↗
PubMed1986

A fully automated immuno-turbidimetric determination of fibrin(ogen) degradation products.

A fully automated procedure for the determination of fibrin(ogen) degradation products was developed using the I. L. Multistat Centrifugal Analyzer (MCA). The assay is based on the turbidometric measurement of the interaction between antibodies to human fibrinogen and defibrinogenated specimens. The method allows, with high reproducibility, for the accurate quantitation of degradation products between 10 and 160 micrograms/ml. A comparative study of 100 normal and abnormal patient samples revealed an excellent correlation with the semi-quantitative manual procedure. The method can be adapted to existing automated coagulation procedures and can become part of coagulation panels.

Antibodies↗
PubMed1985

A fully automated method for clot based coagulation panels using an MCA Multistat Centrifugal Analyzer.

Small modifications of the commercially available software of the I.L. Multistat Centrifugal Analyzer (MCA) enabled us to evaluate clot based prothrombin times (PT), activated partial thromboplastin times (APTT) and thrombin times (TT) simultaneously within one run. This imparted a great deal of flexibility to this procedure in that batches and/or panels of clot based and other types of turbidimetric tests can be performed concurrently in any combination. The PT and TT by this turbidimetric procedure correlated very well with those of the Fibrometer in normal specimens as well as in a wide variety of coagulation defects. The turbidimetric APTT procedure, however, often produced clotting times longer than those achieved with the Fibrometer. The discrepancy between the Fibrometer and turbidimetric APTT procedures was shown to be the consequence of greater sensitivity of the latter to detect low concentrations of heparin, elevated fibrinogen split products and mild factor deficiencies. The available clot based procedures are suitable for use in detecting specific factor deficiencies and the presence of coagulation inhibitors.

Autoanalysis↗
PubMed1982

Kinetic studies on the initial contraction dependent high ATPase activity of actomyosin molecules.

In contracting (superprecipitating) clearing and fully contracted (previously superprecipitated) actomyosin molecules the presteady state phosphate burst was found to be 2 nanomoles inorganic phosphate (Pi) per nanomole myosin. In these muscle models a significant difference in the Mg2+ ATPase activity was found following the initial phosphate burst. Between 120 and 800 milliseconds after the commencement of the reaction the Mg2+ ATPase activity of contracting actomyosin molecules was 5-10 times greater than that of the fully contracted or clearing actomyosin molecules. In the same time interval the rate of turbidity increase of the contracting actomyosin molecules was about 10 fold greater than during the remainder of the time to reach maximal superprecipitation. This high initial ATPase activity found to be present only in the contracting actomyosin molecules and coinciding with the high rate of the velocity of contraction provides sufficient energy for contraction. We propose that this high Mg2+--ATPase activity following the initial burst and included as a part of "conventional" steady state ATPase activity is the source of energy for muscular contraction. Calculation of kinetic and thermodynamic constants indicates that the contracting actomyosin molecule is subjected to a conformational change. As a consequence of contraction the complementarity of the enzyme site to the intermediate complex decreases about 100 fold. Thus the contracted molecules temporarily become relatively refractive to provide energy for the contractile process. In our opinion these findings are important with regard to muscular contraction.

Actomyosin↗
PubMed1982

Comparative studies on the enzymological and contractile properties of glycerinated muscle fibers and actomyosin suspensions.

Kinetic parameters of enzymatic reactions and contractile responses induced by adenosine triphosphate were studied using actomyosin suspensions or glycerinated muscle fibers. The results showed excellent correlations between the enzymatic and contractile events in both muscle models. Based on comparison of the kinetic constants of the two models, it is proposed that superprecipitation and supercontraction are similar expressions of an ATP-induced contractile response in muscle models of various levels of organization.

Actomyosin↗
PubMed1979

Interaction of actin with myosin A and heavy meromyosin.

Ca2+ "free" actomyosin suspensions as well as actin heavy meromyosin (HMM) solutions in the presence of Ca2+ showed no contractile response (superprecipitation) and had low steady-state Mg2+-ATPase activity. Under the same experimental conditions both the enzymatic activity increased and contractile response was restored if the solubility of the proteins was depressed by the addition of polyethylene glycol 4000 (PEG-4000). The stability of the enzymatically active actomyosin or actin HMM complexes was 10 times lower in cleared solutions than in the insoluble actomyosin or actin HMM suspensions. It was concluded that soluble actomyosin or actin HMM solutions are inadequate test tube models for studying muscular contraction.

Adenosine Triphosphatases↗
PubMed1975

Enzymatic studies on the skeletal myosin A and actomyosin of aging rats.

Myosin A and actomyosin were isolated from the skeletal muscle of old and young rats. The velocity of the Ca2+ activated myosin A ATPase was increased in the case of the older animals. On the other hand the velocity of the Mg-2plus activated actomyosin ATPase was decreased in the skeletal muscle of the aging rats. At 5 X 10-5M EGTA concentration the inhibition of the Mg-2plus activated myosin B ATPase of the 1-month-old rats was two- to threefold smaller than that of the older animals. It was shown that the myosin A component of the actomyosin was responsible for the decreased troponin inhibition in the case of the 1-month-old rats. Between the ages of 1 month and 29 months the number of free myosin A SH groups decreases by 50%. The lipid peroxidation in the muscle of the 1-month-old animals.

Actins↗
PubMed1975

Effect of trinitrophenylation on the correlation between ATPase activity and superprecipitation of skeletal actomyosins.

The results of this work have shown that the actin-induced increase of the presteadystate extraphosphate production is depressed in the case of the trinitrophenylated myosin A. At the same time the onset of superprecipitation is delayed and the rate of turbidity change of the trinitrophenylated synthetic actomyosins is depressed significanylt. The results of these experiments failed to demonstrate any correlation between the steadystate ATPase activity of myosin A or actomyosin enzyme and the onset and rate of the superpricipitation reactions. The results of this study seem to indicate that the time resolution of the instruments used to monitor the turbidity changes during the superprecipitation reaction may be an important factor in the proper evaluation of the experimental results.

Actins↗