Resting muscle levels and the influence of exercise on serum amino acid-arylpeptidase activity in man.

Activities of amino acid arylamidases in skeletal muscle and serum of healthy male subjects were investigated using various substrates (Ala-, Leu-, Phe- and S-benxylcysteine-4-nitroanilides). At rest, there is no agreement between muscle and serum activity patterns. After physical exercise, the serum increase of Ala-, Leu- and Phe-AP activities is closely correleated to their respective activities in resting muscles. Since there is no relationship of the postexercise increase of amino acid arylpeptidase activitiy and exercise-induced intrasvascular haemolysis, it appears highly probable that the origin of the serum activity increase after physical work is skeletal muscle.