Biol. Pharm. Bull. 27(5) 691—693 (2004)

sis saturnus var. mrakii IFO 0895, is a strong anti-yeast protein and belongs to the K9-type killer toxin group. HM-1 consists of 88 amino acids and is stable to heat treatment and various pH conditions. The three-dimensional structure of HM-1 has been elucidated using nuclear magnetic resonance. The interactions of HM-1 with sensitive yeast are evaluated in two steps: an initial binding to cell-wall polysaccharides and a secondary binding to its receptor localized in the cell membrane. HM-1 interferes with the cell-wall synthesis of sensitive cells through inhibition of b-1,3-glucan synthase, and forms pores at the budding tips of dividing cells following the spouting of cellular materials leading to cell death. Through these processes, two specific arginine residues of HM-1, Arg-82 and Arg-86, are required for the cytocidal effect on yeast Saccharomyces cerevisiae. In addition to these properties, the unique property of HM-1 was its inability to destroy the spheroplasts of sensitive yeast cells. But the morphology of spheroplasts was affected by HM-1, resulting in a perfectly round shape with an increase in the volume and cellular vacuoles. In the present study, two purified monoclonal antibodies, 1F1 and 4A2, and ployclonal antiserum were prepared to establish quantitative determination of HM-1 by sandwich enzyme-linked immunosorbent assay (ELISA). The characterizations of two monoclonal antibodies were carried out, and the sandwich ELISA of HM-1 was established to quantitate HM-1 and its analogues produced by a mutant HM-1 genebearing yeasts into culture broth.