Comparison of the specificity and kinetic properties of 3 milk-clotting enzymes

Selected achievements of the Central Food Research Institute, Budapest, from its establishment until the turn of the 21 st century

The treatise provides selected examples on the activities and main results of the research and development work during the first forty years of history of the Central Food Research Institute, Budapest.

Use of Platelet Aggregometer to monitor the chymosin-initiated coagulation of casein micelles

The chymosin-initiated coagulation of casein micelles was followed by monitoring light transmission using a Platelet Aggregometer. The release of macropeptide by chymosin was monitored using fluorescamine. The lag period in the clotting reaction was proportional to clotting time and the reciprocal of enzyme concentration. The average rate of coagulation, which was approximately equal to the reciprocal of clotting time (Tc), increased in proportion to enzyme concentration at low enzyme concentrations and reached a limiting value at high enzyme concentrations. The percentage hydrolysis at the Tc was 47 ± 5% in the presence of 20 mM-CaCl2 and it was calculated that a 5-fold decrease in the speed of the enzyme-catalysed reaction would decrease this value at the Tc to 43 ± 5%. The possible uses and limitations of the Platelet Aggregometer for determining the influence of the chemical environment on the velocity of the chymosin-catalysed reaction and para-casein micelle aggregatability are discussed.

Kinetic studies on the action of Mucor pusillus, Mucor miehei acid proteases and chymosins A and B on a synthetic chromophoric hexapeptide

The action of two milk-clotting fungal proteases from Mucos pusillus and Mucor miehei and of chymosins A and B on the hexapeptide, Leu-Ser-Phe(NO2)-Nle-Ala-Leu-OMe, and on kappa-casein were studied. The effects of pH and temperature on the initial rates of hydrolysis of the hexapeptide were examined. Crystalline chymosin and M. pusillus protease exhibited optimal activities around 49 and 55 degrees C, respectively, whereas the optimum temperature for M. miehei protease is higher than 63 degrees C. The optimum pH was about 4.7 for both fungal proteases whereas chymosin A and chymosin B exhibited optimal activities around 4.2 and 3.7, respectively. Kinetic parameters were then determined under optimal conditions and/or at pH 4.7. Fungal proteases had kcat/Km ratios that were similar to each other and that were significantly greater than the ratios obtained for the chymosins. Nevertheless, chymosins had much greater clotting activities towards kappa-casein relative to their proteolytic activities towards the synthetic peptide.

Action of rennin on casein. III. Effect of alpha s- and beta-casein on the secondary phase

The action of rennin on kappa-casein was studied as a function of time, employing turbidity measurements at 610 nm and the release of nonprotein nitrogen. kappa-Casein was converted to para-kappa-casein by the action of rennin. The para-kappa-casein aggregated to increase turbidity and then precipitated. Turbidity development was enhanced initially and then retarded severely by increasing concentrations of added alpha s- and beta-casein. The addition of selected amino acids and salts had variable effects on increase of turbidity.

Characterization of byssochlamyopeptidase A

The enzyme properties of byssochlamyopeptidase A, a chymosin-like enzyme produced by Byssochlamys fulva were studied. The enzyme was shown to be electrophoretically and immunochemically pure. Most metallic cations had negligible effect, whereas Hg2+ greatly suppressed the enzyme activity. N-Bromosuccinimide and I2 completely inactivated the enzyme. For milk clotting at pH 4.6-6.6, the enzyme was less sensitive to pH than pepsin. The substrate specificity of the enzyme was studied by incubation of the enzyme at 37 degrees C with whole and individual casein fractions at pH 6.6 and pH 3.0, respectively. The proteolysis by the enzyme was found to be most extensive for alphas-, less for kappa-, and least for beta-casein. Studies with different synthetic dipeptides and tripeptides revealed that byssochlamyopeptidase A exhibits specificity for Phe-Tyr and Gly-Phe-Phe, but the enzyme did not hydrolyze Ac-Phe-Tyr(I2).

Kinetics of pepsin-initiated coagulation of kappa-casein

The kinetics of pepsin initiated coagulation of kappa-casein have been studied at pH 5.8. The primary and secondary phases of coagulation are shown to proceed simultaneously. The theory of enzymatically initiated clotting reactions proposed by Payens (Payens, T.A.J. (1976) Neth. Milk Dairy J. 30, 55--59) has been applied to this clotting system and has been used to obtain rate constants for the secondary phase of coagulation. As expected, clotting rate constants for kappa-casein increase with pepsin concentration. An activation energy of 30.6 kcal/mol has been obtained for the secondary phase of coagulation. Turbidity measurements are a convenient means for studying the secondary phase of coagulation but do not provide an unambiguous means for studying the primary phase of the reaction.

On enzymatic clotting processes. I. Kinetics of enzyme-triggered coagulation reactions

The kinetics of enzymatic clotting reactions such as the clotting of blood or milk, is analyzed. The appearance of a lag phase in the clotting is shown to be due to the difference in reaction order of enzymatic production and flocculation. The weight-average particle weight of the product formed is found to be a quadratic function of the reaction time. The condition for the clotting time is t square root of ksV/2 = C, where t is the clotting time, ks the flocculation rate constant, V the maximum rate of enzymatic product formation and C a constant. In agreement with this result double-logarithmic plots of t versus enzyme dilution are always observed to be linear over a wide range of enzyme concentrations. No statistical evidence could be produced for the widely held belief that the clotting time should be inversely proportional to the enzyme concentration. Varying exponents of the latter in its relation to the clotting time are discussed in terms of von Smoluchowski's theory of the slow coagulation of colloidal particles.