DIFFERENCES IN THE SUBCELLULAR AND SUBSYNAPTOSOMAL DISTRIBUTION OF THE PUTATIVE ENDOPLASMIC-RETICULUM MARKERS, NADPH-CYTOCHROME C REDUCTASE, ESTRONE SULFATE SULFOHYDROLASE AND CDP-CHOLINE-DIACYLGLYCEROL CHOLINEPHOSPHOTRANSFERASE IN RAT-BRAIN

Abstract— A comprehensive study has been undertaken on the subcellular and subsynaptosomal distribution of a number of markers for subcellular organelles in preparations from rat brain. Although the activity of most enzymatic markers was decreased by freezing and storage at ‐ 70oC, no significant changes were noted in the distribution of these activities. This demonstrates that contamination of brain fractions by subcellular organelles can be accurately assessed after freezing and thawing. A marked discrepancy was noted between the distribution of three putative markers for endoplasmic reticulum. CDP‐choline‐diacylglycerol cholinephosphotransferase (EC 2.7.8.1) activity was mainly limited to the microsomal fraction and was present to a lesser extent in the synaptosomal fraction than the other putative markers for endoplasmic reticulum. Estrone sulfate sulfohydrolase (EC 3.1.6.2) activity demonstrated a bimodal distribution between the crude nuclear and microsomal fractions. However, considerable activity was associated with the synaptosomal fraction. NADPH‐cytochrome c reductase (EC 2.3.1.15) activity sedimented in the microsomal and the synaptosomal fractions. Calculations based on the relative specific activities of the microsomal and synaptic plasma membrane fraction indicated that the contamination of the synaptic plasma membranes by endoplasmic reticulum was 44.5% (NADPH‐cytochrome c reductase), 38.0% (estrone sulfatase) and 9.0% (cholinephosphotransferase). Since it is believed that virtually all of the synthesis of phosphatidylcholine by cholinephosphotransferase occurs in the neuronal and glial cell bodies, it was concluded that cholinephosphotransferase is a satisfactory marker for the endoplasmic reticulum derived from these sources. The results suggest that NADPH‐cytochrome c reductase and estrone sulfatase may be present in the smooth endoplasmic reticulum system responsible for the fast transport of macromolecules along the axon to the nerve endings as well as in the endoplasmic reticulum of the cell bodies. The possible relation between that portion of the smooth endoplasmic reticulum involved in fast axonal transport and the GERL (Golgi, Endoplasmic Reticulum, Lysosomes) complex discovered by Novikoff and his coworkers (Novikoff, 1976) is discussed. Copyright © 1979, Wiley Blackwell. All rights reserved