Kinetics for the reaction of microbial transglutaminase (MTG) with individual caseins in a TRIS-acetate buffer at pH 6.0 was evaluated under atmospheric pressure (0.1 MPa) and high pressure (400 MPa) at 40 degrees C. The reaction was monitored under the following limitations: The kinetics from the initial velocities was obtained from nonprogressive enzymatic reactions assuming that the individual catalytic constants of reactive glutamine residues are represented by the reaction between MTG and casein monomers. Enzyme reaction kinetics carried out at 0.1 MPa at 40 degrees C showed Henri-Michaelis-Menten behavior with maximal velocities of 2.7 +/- 0.02 x 10(-3), 0.8 +/- 0.01 x 10(-3), and 1.3 +/- 0.30 x 10(-3) mmol/L.min and K-m values of 59 +/- 2 x 10(-3), 64 +/- 3 x 10(-3), and 50 +/- 2 x 10(-3) mmol/L for beta-, alpha(s1)-, and acid casein, respectively. Enzyme reaction kinetics of beta-casein carried out at 400 MPa and 40 degrees C also showed a Henri-Michaelis-Menten behavior with a similar maximal velocity of 2.5 +/- 0.33 x 10(-3) mmol/L.min, but, comparable to a competitive inhibition, the Km value increased to 144 +/- 34 x 10(-3) mmol/L. The reaction of MTG with alpha(s1)-casein under high pressure did not fit in to Henri-Michaelis-Menten kinetics, indicating the complex influence of pressure on protein-enzyme interactions.