Abstract
The polyisoprenyl phosphate dephosphorylating activity of rat liver has been investigated with regard to substrate specificity, subcellular distribution, and transmembrane orientation. Total liver microsomes were employed as a source of enzymatic activity against a variety of 32P-labeled substrates. Susceptibility to dephosphorylation followed the order solanesyl phosphate > α- cis-polyprenyl 19-phosphate = α- trans-polyprenyl 19-phosphate = dihydrosolanesyl phosphate > ( S)-dolichyl 19-phosphate = ( R)-dolichyl 19-phosphate = ( R,S)-dolichyl 11-phosphate. There appeared to be no major effect of chain length from 11 to 20 isoprenes. Data obtained from inhibition studies using solanesyl [ 32P]phosphate as substrate were consistent with the substrate specificity studies and suggested that a single activity is responsible. With dolichyl [ 32P]phosphate as substrate, the phosphatase specific activity of the subcellular fractions prepared from rat liver was found to follow the sequence Golgi = smooth endoplasmic reticulum > plasma membrane > lysosomes = rough endoplasmic reticulum > nuclei > mitochondria. Transmembrane topography studies, using enzyme latency as a criterion, were consistent with an orientation of the active site facing the cytoplasm.
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