STK1 profile in FPLC fractions of another healthy dog (sample no. 14, See Table1) (A) Serum thymidine kinase 1 (sTK1) activity in the fractions from the healthy dog (•). (B) Western blot analyses of sTK1 protein in the same fractions. Arrows indicate the elution position of the molecular weight (MW) markers. Numbers represent the fast protein liquid chromatography (FPLC) fractions.