NEW MATERIAL:An isoleucin-linking factor (active to link isoleucin to a protein; capable of specifically bonding isoleucin among amino acids; optimum pH of the linking reaction of isoleucin and protein, 8.5W9.0; molecular weight, about 60,000; adsorptive to phosphocellulose and hydroxyapatite; resistant to the treatment with deoxyribonuclease and ribonuclease; exhibits little inactivation by the treatment with chymotrypsin and trypsin; deactivated by the heat-treatment at 90°C for 1min).

USE: It facilitates the linkage of isoleucin to a protein and is applicable for the control of conception and the efficient mating, etc.

PREPARATION: Sperm of swine, bovine, rabbit, etc., is disintegrated with a sonicator, etc., and centrifuged to obtain a crude extract. The extract is purified to about 1,000 times by the column chromatography using phosphocellulose, etc., to obtain the objective isoleucin-linking factor.