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Peptidase Activity in the Thymus of a Normal and a Leukemic Strain of Mice during Growth and Aging^*

( Gerontologic Unit, Allan Memorial Institute, Department of Psychiatry, McGill University, Montreal, Canada)

1. The characteristics of hydrolysis of triglycine by thymus homogenates from normal mice were investigated. The course of hydrolysis with time proceeds according to first order kinetics. At tissue concentrations between 1 and 6 mg/ml, the rate of hydrolysis is proportional to the tissue concentration. The pH optimum lies around pH 7.0. In the presence of cobalt, the rate of hydrolysis is increased, and more than one bond of the tripeptide is split. Magnesium and manganese have, if anything, a slight inhibitory effect.

2. In normal Rockland (RAP) mice the peptidase activity of the thymus per unit weight of tissue, measured by the rate of hydrolysis of triglycine in vitro, decreases with the age of the animal.

3. The average peptidase activity of the thymus is significantly higher in Akr than in RAP mice. This difference was found to be greatest, and the highest values in the Akr strain were obtained, at the age period when most of the Akr mice spontaneously develop acute lymphocytic leukemia. However, in animals under 1 month old, the values of the Akr strain were also significantly higher than those of the normal (RAP) strain.

4. There is no significant difference between the peptidase activity of the thymi from Akr mice which had developed spontaneous lymphocytic leukemia and that of apparently healthy Akr mice. The activity with both types of Akr mice varied greatly and ranged from normal to about 2 times the normal value.

5. The significance of these findings is discussed.

^* This work was supported by a grant from the National Cancer Institute of Canada to Dr. Bernard Grad of the Gerontologic Unit, Allan Memorial Institute, Department of Psychiatry, McGill University, Montreal.

Received 12/24/53.