The dependence of pump-induced hyperpolarization on the tonicity of the surrounding medium and intracellular sodium concentration

Inhibition of rat liver and kidney arginase by cadmium ion

Cadmium ion activates arginase from many species of organisms but is an inhibitor of arginase from many other species. The purpose of this study was to investigate the inhibition of rat liver and kidney arginase by cadmium ion. Rat kidney arginase was inhibited by much lower concentrations of cadmium ion than rat liver arginase. Cadmium ion was a mixed noncompetitive inhibitor of both rat liver and kidney arginase. Cadmium ion enhanced the substrate activation of rat kidney arginase while still inhibiting the enzyme. Cadmium ion prevented the substrate inhibition of rat kidney arginase by fluoride while still inhibiting the enzyme. Cadmium ion also inhibited rat kidney arginase in the presence of manganese ion.

Purification and kinetic properties of Mus booduga (Gray) hepatic arginase

Hepatic L-arginase from the Mus booduga (Gray) was purified and its kinetic characteristics were investigated. The enzyme was not adsorbed on DEAE-cellulose, but was retained on CM-cellulose column at pH 7.2. The Michaelis-Menten constant was 8.3 mM for L-arginine and was independent of pH in the range of 7.5-10.5. L-arginine concentrations as high as 0.4 M did not exert substrate inhibition in the pH range 7.4-10.0. Manganese was required at a concentration of 0.05 M for full activation of the enzyme. L-ornithine and L-lysine inhibited the enzyme competitively with inhibitory constants of 1.9 mM and 3.7 mM respectively. Several properties of the L-arginase from Mus booduga clearly identify it as an enzyme similar to ureotelic basic arginases from mammalian liver.

Kinetics and inhibition by some aminoacids of lactating rat mammary gland arginase

Some kinetic and regulatory properties of lactating rat mammary gland arginase were studied. At pH 7.4, i.e. at near-physiological conditions, there was evidence of inhibition by excess of substrate, with a Km value of 9.5 mM, slightly lower than the value of 18 mM observed at pH 9.8 (maximum enzyme activity). A study was also made of the effects of proline, ornithine, lysine and certain branched-chain aminoacids on enzyme activity: lactating rat mammary gland arginase was strongly and competitively inhibited by lysine, ornithine and valine, with Ki values of 1.2 mM, 1.1 mM and 3.6 mM, respectively. Other aminoacids (proline, isoleucine and leucine) also inhibited lactating rat mammary gland arginase, although to a lesser extent.

Gel filtration behaviour of arginase in frog liver and kidney extracts

The molecular weight of arginase, determined by gel filtration of frog (Rana tigerina) liver and kidney extracts, varied with the protein concentration. It increased from about 25-27 KDa in dilute solutions to about 92-96 KDA in concentrated extracts. In addition, an arginase with a molecular weight of 45-49 KDA appeared at intermediate concentrations. The results suggest the probable aggregation of arginase monomers to yield the dimeric and tetrameric forms of the enzyme at high protein concentration in extracts.

Purification and properties of liver arginase from teleostean fish Clarias batrachus (L.)

Liver arginase of Clarias batrachus has been purified to 56.3-fold employing ammonium sulphate fraction, DEAE-cellulose and CM-cellulose chromatography. Bidirectional polyacrylamide gel electrophoresis shows the presence of two isoenzymes of arginase. The enzyme has a molecular weight of about 87,000 and Km 15.38 mM for L-arginine, optimum pH 9.5 and temperature 37 degrees C. Ornithine and leucine as competitive whereas valine and isoleucine act as non-competitive inhibitors with respect to L-arginine as substrate.

The changes in CiNa of sheep cardiac Purkinje fibres in hyperosmotic solutions

1. The changes in intracellular sodium ion concentration (CiNa) of sheep cardiac Purkinje fibres in hyperosmotic solutions were studied using Na-sensitive liquid ion-exchanger microelectrodes. 2. CiNa was increased in hyperosmotic solutions containing different concentrations of sucrose from 0 to 300 mM. 3. The changes in resting membrane potential (RMP) in hyperosmotic solutions had no regularity. In most of the experiments there was hyperpolarization of the membrane but in a few cases a depolarization or no change of RMP were also observed. 4. The N-shape of I-V relations of the fibres became more pronounced in hyperosomotic solutions.