On the mechanism of enzyme acition. XLVI. The effect of certain ions on crystalline trypsin and reinvestigation of its isoelectric point

Calcium and manganese ions are effective protectors of crystalline trypsin in alkaline solutions. Other ions seem to have no significant influence. The effect of calcium is due to a decrease in the rate of autodigestion of trypsin but does not affect the rate of tryptic digestion of other proteins.The isoelectric point of trypsin is in the neighborhood of pH 11, as determined by electrophoresis analyses. This high isoelectric point is correlated with the amino acid composition of trypsin and its amide nitrogen content.     

The kinetics and thermodynamics of reversible denaturation of crystalline soybean trypsin inhibitor

Crystalline soybean trypsin inhibitor protein undergoes denaturation on heating which is reversed on cooling. In the range of temperature of 35 to 50 degrees C. a solution of the protein consists of a mixture of native and denatured forms in equilibrium with each other. The equilibrium is only slowly established and its final value at any temperature is the same whether a heated, denatured solution of the protein is cooled to the given temperature or whether a fresh solution is raised to that temperature. The kinetics of reversible denaturation of the soybean protein as well as the reversal of denaturation is that of a reversible unimolecular reaction, each process consisting at a given temperature of the same two simultaneous reactions acting in opposite directions. The experimental data on the effect of temperature on the velocity and the equilibrium constants of the opposing reaction were utilized in evaluating the reaction energies and activation energies. The reaction energies for denaturation were found to be as follows:- Change in total heat of reaction DeltaH = 57,000 calories per mole Change in entropy of reaction DeltaS = 180 calories per degree per mole The heat of activation DeltaH(1) (double dagger) for denaturation = 55,000 The heat of activation DeltaH(2) (double dagger) for the reversal of denaturation = -1900 The entropy DeltaS(1) (double dagger) for denaturation = 95 The entropy DeltaS(2) (double dagger) for reversal of denaturation = -84     

The influence of Li+ ions on pepsin and trypsin activity in vitro

BackgroundThe paper presents a study on the influence of different lithium carbonate and lithium citrate concentration on proteolytic enzymes, namely pepsin and trypsin, in vitro. Lithium can directly affect enzyme activity. Its influence on many bodily functions in both ill and healthy people has been proven.MethodsTo assess the influence of Li⁺ ions concentration and the substrate/enzyme ratio on pepsin and trypsin activity in vitro, 60 factorial experiments were conducted (each repeated 30 times).Main findingsFor both enzymes, statistically significant changes in their activity under the influence of lihium carbonate and lithium citrate were observed. The biggest increase in enzyme activity reached even 198.6 % and the largest decrease in enzyme activity reached about 50 %.ConclusionsThe study shows that both organic and inorganic forms of lithium salts cause changes in the activity of digestive enzymes. Different concentrations of lithium carbonate and lithium citrate stimulate or inhibit the activity of trypsin and pepsin.     

The effect of trypsin on membrane transport of non-electrolytes

Trypsinization of alveolar macrophages depresses lysine transport but has no effect on nucleoside transport. The depression of the initial rate of lysine transport is due to a decreased rate of exchange diffusion presumably secondary to lowered intracellular pools of amino acids. It is shown directly that trypsinization accelerates the efflux of amino acids but not certain other metabolites, and reduces the capacity of the cell to concentrate amino acids.     

The effect of trypsin treatment on rabbit muscle phosphofructokinase

The consequences of trypsin treatment of rabbit muscle phosphofructokinase, in terms of the physical and kinetic properties of the enzyme, have been investigated. At 1% trypsin (w/w) and 25 °C, no activity is lost over a period of 60 min. The complex sedimentation behavior at pH 8 (three peaks) is unchanged by this treatment as is the extent of dissociation of the enzyme when the pH is lowered from 8 to 6 or reassociation when the pH is raised back to 8. However, the trypsin-treated enzyme shows a subunit molecular weight, determined in the guanidine HCl or 0.5 m acetic acid, of 35,000–40,000 compared to the subunit molecular weight of the untreated enzyme at 75,000–80,000. Similarly, SDS gels give only a single species of about 80,000 for the native enzyme but two species, 42,000 and 48,000, for the trypsin-treated enzyme. Kinetic studies showed no differences in the regulatory properties of the enzyme including fructose 6-phosphate cooperativity, ATP inhibition, NH_4⁺ activation, and cAMP activation. Small differences in stability and inhibition by citrate and creatine phosphate were observed.