Fig. 2.

The variation of DHFR activity in individual human livers and comparison of its average value to that in rat liver. (A) The activity of DHFR in the liver of 6 human subjects determined with 7,8-DHF as substrate. Subjects 1–5 were organ donors; 1 was a victim of smoke inhalation and 2–5 were from automobile accidents. Liver tissue samples from these subjects were frozen immediately and later extracted. Normal liver tissue was obtained from subject 6 during surgery for removal of a benign hepatoma and was extracted immediately without prior freezing. Homogenates of at least 2 separate samples from the liver of subjects 1–4 were examined. For both subjects 5 and 6 a single homogenate of at least 50 g of tissue was prepared. n = the total number of reactions with at least 4 time points in each. (B) Comparison of the average DHFR activity in human liver with the average value in rat liver.