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NUCLEOSIDE DIPHOSPHATASE AND THIAMINE PYROPHOSPHATASE ACTIVITIES IN THE ENDOPLASMIC RETICULUM AND GOLGI APPARATUS

The effects of pH, fixatives and divalent ions on nucleoside diphosphatase (NDPase) and thiamine pyrophosphatase (TPPase) activities in the endoplasmic reticulum (ER) and Golgi apparatus (GA) were examined in adult and neonatal hepatocytes and other cell types in the rat. In liver cells TPPase and NDPase both have a similar localization in the rough ER, nuclear envelope and smooth ER but differ in their pH optima; TPPase is most active at pH 8, NDPase at pH 7. TPPase in the GA, unlike its counterpart in the ER, is most active at neutral pH. High levels of NDPase activity are present in the GA of neurons, epididymis and other cells, but not in hepatocytes. TPPase in the ER, but not the GA, is stimulated by the addition of adenosine triphosphate to the medium. These observations show that different conditions are required to demonstrate ER and GA diphosphatase activities. Whether separate enzymes or multiple configurations of a single protein are responsible for these activities cannot be determined by staining procedures.