Transpeptidation as the main chemical reaction causing the formation of plasteins

Abstract

AbstractIn the wide range of the experimental conditions transpeptidation was shown to be an only chemical reaction causing the plastein structure formation. This standpoint is supported by the estimations of the number‐average molecular weights of the reaction mixture and by the measurements of the quantity of trichloroacetic acid‐precipitated fractions. Phenomenologically transpeptidation results in the increase of the reaction mixture viscosity. This process has two steps with different characteristic times. During the first step, lasted for several minutes, enzyme catalysed transpeptidation occurs. The second step, lasted for several days, is characterized by the non‐covalent interaction of the polypeptides formed during the first step. The investigation of the plasteins with the help of transmission and scanning electron microscopy shows that in plastein reactions the aggregation of peptides takes place resulted in the formation of sponge‐like plasteins. The study of peptide bond thermodynamics of the model peptides and of the kinetics of protease‐catalysed acyl‐transfer shows that in our case transpeptidation is the result of the kinetic but not thermodynamic reasons.