The lysozyme of bacteriophage phi IN93 was purified to apparent homogeneity with Carboxymethyl Sepharose and Hydroxyapatie columns from lysates of the phage grown on Thermus aquaticus TZ2. The enzyme is a single polypeptide chain with a molecular weight of 33,000. From the determined N-terminal amio acids of the enzyme, the locus of the gene was specified on a phi IN93 genome. The enzyme was not similar to egg white lysozyme. T4 phage lysozyme, or lambda phage lysozyme. The enzyme, pIN93 lysozyme, was found to be a novel type of thermophilic lysozyme, which lyses specifically Thermus sp. cells, and exhibited conspicuous thermal stability at 95 degrees C for 1 h in the presence of beta-mercaptoethanol. (C) 2008 Elsevier Inc. All rights reserved.