A bacteriocin was prepared from the in-duced lysate of Pseudomonas aeruginosa as a homogeneous, high molecular protein. Elec-trophoretic mobility, sedimentation constant and the amino acid composition were deter-mined. Electron microscopy showed a close similarity of the pyocin to phage tail.
The author expresses his heartily thanks to Dr. Y. Homma, Institute for Infections Deseases, Univer-sity of Tokyo, for the gift of bacterial strains, Dr. S. Kinoshita, Kyowa Hakko Kogyo Co., Tokyo, for the gift of mitomycin C, Dr. Ui and Dr. Tarutani of Gumma University, Maebashi, for the measurement of sedimentation constant, Dr. S. Murakami, College of General Education, University of Tokyo, for electron-microscopy, and Mr. S. Horiuchi of this
department for the amino acid analysis. Thanks are also due to Mrs. K. Ikeda for her held and Professor F. Egami for his guidance and encouragement throu-ghout this work.