In this paper, TPK activity from human peripheral blood lymphocyte membrane was measured using synthetic PGAT as substrate. The kinase activity was more strongly inhibited by a synthetic compound,1-isopropyl-6-amino-thieno (3,4-d) pyrimidine-2, 4-dione (IATPD); IC₅₀ was about 300μmol/L. Lineweaver-Burk plots revealed that IATPD was competitively with ATP and noncompetitively with PGAT to inhibit the kinase activity.