Biomedical subjects

S Guinand

Publications and source records attributed to S Guinand.

3 recordsLinked to original sources

PubMed1979

Magnesium ion dependent adenosine triphosphatase activity of heavy meromyosin as a function of temperature between +20 and -15 degrees C.

The hydrolysis of Mg2+-adenosine 5'-triphosphate (ATP) by heavy meromyosin has been studied between +20 and -15 degrees C, especially in the low-temperature range, in a medium containing 30% (v/v) ethylene glycol by fluorometric, spectrophotometric, and potentiometric measurements. The time course of the fluorescence changes of the enzyme during the reaction depends markedly on the temperature in consequence of large differences between the activation energies of the various steps. The observed kinetics have been analyzed according to the simplified scheme of Bagshaw & Trentham [Bagshaw, C. R., & Trentham, D. R. (1974) Biochem. J. 141, 331-349]. The following results have been obtained. (1) The rate-limiting step of the reaction changes in this temperature range; at 20 degrees C M**.ADP.Pi is the predominant steady-state complex, and M*.ADP predominates at -15 degrees C, with a half-life of approximately 10 min. (2) As expected, on the basis that it is the dissociation of the M*.ADP complex which becomes rate limiting at low temperature, one observes, in the pre-steady-state below 0 degrees C, both a proton burst and a lag phase in ADP release. (3) At low temperature, the equilibrium M*.ATP in equilibrium M**.ADP.Pi is displaced to the left All the kinetic data obtained in this study are compatible with a simple pathway for the Mg2+-ATP hydrolysis by myosin and with sequential release of the reaction products.

Adenosine Triphosphatases↗

PubMed1978

[Model of the interaction between trypsin and alpha 2-macroglobulin of porcine serum].

A comparative study of the dissociation into subunits of Porcine alpha2 M, either native or bound to trypsin (Tn), has been carried out in order to determine the modifications of the alpha2 M structure due to the formation of the Tn-alpha2 M complex. Analytical ultra-centrifugation at pH 3.5 shows that the dissociation is smaller when alpha 2 M is bound to trypsin. Electrophoresis in 4% polyacrylamide gels, in presence of 0.1% SDS, of alpha2 M and Tn-alpha2 M incubated in 1% SDS leads to the same conclusion; the enzyme must stabilize the quaternay structure of alpha2 M. In presence of SDS + beta-mercaptoethanol, only a molecular weight (M.W.) 200,000 band is revealed in electrophoresis pattern of native alpha2 M. In the case of reduced Tn-alpha2 M, some other bands of M.W. 100,000, 50,000, 30,000 appear. When trypsin is inactivated by TLCK 100,000 M.W. band is present, accompanied by the 200,000 M.W. band whose intensity is function of the alpha2 M concentration. The 100,000 M.W. band appears therefore characteristic of the formation of the complex which must imply a proteolytic cleavage in the middle of the 100,000 polypeptidic chain of alpha2 M. A model of the complex is proposed in which the enzyme forms a proteic bridge between the two halves of the alpha2 M molecule.

Animals↗

PubMed1976

[Study of the complex between porcine plasmin and alpha2-macroglobulin (author's transl)].

Porcine plasmin (EC 3.4.21.7) is obtained from plasminogen activated by human urokinase. This enzyme can bind, in an equimolecular ratio, to an alpha2-macroglobulin isolated from porcine serum. The number of active sites of plasmin has been determined through a burst titration of nitroaniline during the presteady-state hydrolysis of an amide substrate (N-alpha-carbobenzoxy-L-arginine-p-nitroanilide). The kinetic constants relative to a very sensitive ester substrate (N-alpha-carbobenzoxy-L-lysine nitrophenylester) hydrolysis have been measured. The binding of plasmin to alpha2-macroglobulin results in a complete inhibition of proteolytic activity, a reduction of active sites number and a decrease of esterolytic activity towards this substrate. In the complex, the residual activity (about 60%) is protected from protein inhibitors. Absorbance difference spectra show that 1 mol of alpha2-macroglobulin binds 1 mol of plasmin and 2 mol of trypsin. When plasmin is first bound to alpha2-macroglobulin, only 1 mol of trypsin can gain access tothe second site without removing the plasmin, showing that a steric hindrance is implicated in the inhibition performed by alpha2-macroglobulin binding.

Allosteric Site↗