Figure 2

Subcellular distribution of TPP and TPK activity. The nuclear (N), heavy mitochondrial (M), light mitochondrial (L), microsomal (P) and cytosolic (S) fractions, obtained by fractionation of a fresh rat liver homogenate, were analyzed for TPP content (panel A), TPK activity (panel B) and lactate dehydrogenase, marker enzyme for cytosol (panel C, LDH) and other marker enzymes (data not shown). Results are expressed as relative specific activities versus percentage of total protein. Relative specific activity is defined as the percentage of total recovered activity present in a particular fraction divided by the corresponding percentage of protein. Recoveries for TPP content (23 nmol/g liver) and LDH (456 U/g liver) and TPK (263 nmol/g liver/h) activities were 128%, 97% and 97%, respectively. Recoveries for GDH activity and protein content were 102% and 94%, respectively (data not shown). A second fractionation (data not shown) resulted in a similar histogram for TPP (28 nmol/g liver), but with somewhat more enrichment in the M-fraction (RSA 1.79) (recovery 108%); other marker enzyme and protein recoveries varied between 70% to 102%. The TPP measured in the N-fraction is partially due to unbroken and damaged cells, which are pelleted together with nuclei.