Highly stabilized papain conjugated with water‐soluble phospholipid polymer chain having a reacting terminal group

Abstract

AbstractA novel water‐soluble and biocompatible phospholipid polymer, poly(2‐methacryloyloxyethyl phosphorylcholine) (PMPC), was synthesized using a photoinduced living radical polymerization technique for modification of the enzyme. The PMPC had a reactive carboxylic group on a terminal, and its molecular weight and molecular weight distribution were regulated. The PMPC was reacted with the amino groups of papain via amide bonds to form a conjugate (P‐PMPC). The modification degrees with PMPC chains on the conjugate were 22% (P‐PMPC22) and 42% (P‐PMPC42) versus the total number of amino groups of papain. The stability of the P‐PMPC was evaluated in a buffered solution (pH 6.1) at 25 and 40°C. The helix content of the P‐PMPC was slightly below that of native papain. However, the secondary structure of the P‐PMPC was maintained at its initial level for 28 days at both temperatures. The enzymatic activity after the conjugation was about 40% of the native enzyme, but it was maintained about over 75% of the initial enzymatic activity even when it was stored at 40°C for 28 days. This result is due to inhibition of self‐digestion and a change in the ternary structure of papain by the PMPC chains. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 827–832, 2004