It is shown that the peculiar to the malignant growth protein isolated from blood of cattle suffering from leukosis is more stable to the effect of papain than the human protein characteristic of the malignant growth. Papain breaks the studied protein up into three components, the sedimentation constants of Fab- and Fc-fragments isolated from the papain hydrolysate are 3,9 and 3,6S and their molecular mass --55000 and 45000 Daltons, respectively. In the Fab-fragment the contents of lysine, glutaminic acid, leucine, serine are higher and those of arginine, alanine, valine, methionine, phenylalanine and isoleucine are lower as compared with the Fab-fragment isolated from immunoglobulin G of healthy animals. The content of amino acids changes more significantly in the Fab-fragment that in the unsplitted molecule of the protein under study. The polar-to-nonpolar amino acids ratio is 2.27 for the Fab-fragment and 2.48 for the unsplitted molecule. For the same structures of protein isolated from immunoglobulin G of health animals these values are 1.80 and 2.24, respectively. Evidently, peculiarities of the specific to the malignant growth protein isolated from blood of cattle suffering from leukosis are characteristic mainly of its Fab-fragment.
