The acid phosphatase activity of rat liver homogenates and of nuclear and cytoplasmic fractions isolated therefrom (by differential centrifugation) was determined biochemically in a series of experiments. For each liver, Gomori's histochemical test for acid phosphatase was run in parallel.

No correlation was found between the biochemical and the histochemical results. According to the former, the enzyme appears to be almost entirely (95 per cent) located in the cytoplasm, while according to the latter, the acid phosphatase is predominantly concentrated in the nuclei and in some peribiliary polymorphic structures identified as myelin figures.

It was found that the precipitaion pattern obtained in the histochemical test does not reveal, as generally assumed, differences in enzyme concentration among the various cell structures, but actually reveals differences in their lead phosphatase affinity. The usefulnes of the histochemical test for intracellular localization studies was found to be further limited by considerable fixation damage and formation of myelin figure artifacts.

The biochemical approach is to be preferred because of better preservation of the material and direct and more reliable methods for the demonstraton of enzyme activity.

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