The nuclear basic proteins of human testes and ejaculated spermatozoa

Human testicular nuclei were fractionated into two fractions according to their sedimentation in a sucrose density gradient. The nuclear basic proteins isolated from these two fractions were similar and also resembled electrophoretic mobilities and amino acid composition of the liver histones. Only quantitative differences among histone electrophoretic bands were observed. The nuclear basic proteins of ejaculated spermatozoa differed totally from those of the testes. The proteins could be divided into two categories on the basis of their electrophoretic mobilities, molecular weights and amino acid compositions. One group (SpH) was similar to testicular histones; another (HP) group was smaller, with nearly twice the electrophoretic mobility and a much higher arginine content. These proteins (HP) represent a new type of nuclear basic protein found in human tissues.