PURPOSE: To produce an enzyme having specific physical and chemical properties and high activity and stability by extracting and separating from the cell of bacterium of genus Bifidobacterium which is an obligate anaerobe.

CONSTITUTION: Bifidobacterium brebe YIT4006 (FERM BP-752) which is an obligate anaerose separated from human feces is cultured in a conventional medium and the cells are collected by centrifugal separation. The cells are suspended in a buffer solution, treated with lysozyme and subjected to ultrasonic disintegration and ultracentrifugal separation to obtain the supernatant as a crude enzyme liquid. After removing nucleic acids, the liquid is subjected to dialysis, etc. An enzyme having specific physical and chemical properties such as specific action to a closed loop double chain DNA having negative twist can be separated and purified from the above liquid by conventional process. The process has an advantage of enabling the production of an enzyme having high enzymatic activity and high stability on an industrial scale in high yield.