Abstract
The addition of purified luteinizing hormone to isolated rat testis microsomes causes an increase in the activity of the enzyme system that converts 17alpha-hydroxyprogesterone into C(19) steroids in these tissue organelles. The gonadotrophin does not act in this system by altering the Michaelis constants of the enzyme for either steroid or nicotinamide nucleotide, but rather appears specifically to increase the catalytic capability of the protein.