Studies on the Catalytic Action of Poly-α-Amino Acids<subtitle>III. Hydrolysis of <italic>p</italic>-Nitrophenyl Acetate by the Copolymer of Tryptophan and Glutamic Acid <xref ref-type="fn" rid="fn1"><sup>*</sup></xref></subtitle>

Abstract

The hydrolysis of p-nitrophenyl aceptate (NPA) was catalytically promoted by the synthetic copoly (DL-Trp, L-Glu 1: 9). The pH and temperature dependence of the rate of hydrolysis were given as a bell-shaped curve, in which the optimum pH and the optimum temperature were observed at 5.95 and 40° C, respectively. Although copoly (DL-Trp, L-Glu 1: 9) showed activity to NPA, copoly (L-Trp, L-Glu 1: 9) did not show any activity. The apparent maximum velocity (Vmax) and the apparent Michaelis constant (Km) were; Vmax= 1.5 ×l0-6mole/min/mg, Km=2.1 × 10-3M. The order of Km was the same as that of enzyme, but the value of Vmax was considerably low. So the capture of substrate by an active center of the copolymer may be the same order as that of enzyme, however, the copolymer-product complex may be too stable to be hydrolyzed into p-nitrophenol. The following process for the hydrolysis of NPA by copoly-(DL-Trp, L-Glu 1: 9) may be speculated from the results of fluorescence titration, optical rotatory dispersion, rigidity measurement and infrared spectrum; 1) the orientation of substrate is given by tryptophanyl residues. 2) the substrate is hydrolyzed by acid-base interaction of COOH and COO- groups (27). 3) the removal of the products from active center is proceeded by the equilibrium of ENP⇌E+NPOH, where E is copolymer, ENP is copolymer-product complex and NPOH is product (p-nitrophenol).