Abstract
1. In the Padykula-Herman staining medium, only 20% of the adenosine triphosphatase (ATP-ase) activity of rat liver homogenate is manifested, because of inhibition by the high level of calcium.
2. In the Wachstein-Meisel staining medium, only 15% of the ATP-ase activity is manifested, because of the high lead to ATP ratio.
3. The distribution patterns of the residual activity among the isolated subcellular fractions show it to be ATP-ase rather than non-specific phosphatase.
4. Cold formol-calcium fixation (33½-23 hours) reduces the adenosine triphosphatase activity of pieces of liver by 85-90%. The reduction is somewhat less when suspensions (homogenates) are fixed. The loss in activity due to fixation is much greater for the mitochondrial than for the nuclear fraction.
5. We have found the unmodified Wachstein-Meisel technique to give more reliable and consistent staining than any other method tried.
6. Chemical data show the mitochondria to be the major site of ATP-ase activity in rat liver; staining results are not inconsistent with this finding.
7. Staining results show the ATP-ase activity of the nuclear fraction to reside in the bile canaliculi and mitochondria present in the fraction.
8. There is no evidence that the nuclei of rat liver possess adenosine triphosphatase; 5'-nucleotidase activity is indicated with the calcium staining procedure at alkaline pH, but not with the lead procedure at pH 7.2.
9. The possible significance of high ATP-ase activity in the bile canaliculi and portal vessels is considered briefly.