CMP-N-acetylneuraminic acid: Is it synthesized in the nucleus

RadioactiveN-acetylmannosamine was injected intravenously into rats to labelN-acetylneuraminic acid (NeuAc) and CMP-NeuAc. Nuclei were isolated from the livers using a non-aqueous technique to prevent leakage of polar metabolites. A preparation was obtained, which was eight times enriched in nuclei based on the ratio DNA/RNA. Free NeuAc and CMP-NeuAc were isolated from this nuclear fraction and from whole liver, and the specific radioactivities were determined. It appeared that at all time points studied, i.e. 1.5, 9.5, and 18 min after injection, the specific radioactivities of free NeuAc as well as of CMP-NeuAc in the nuclear preparation were lower than those in whole liver. Also no significant differences were found between free NeuAc and CMP-NeuAc in the ratio of specific radioactivities in the nuclear fraction/whole liver. Furthermore, no enzyme involved in the synthesis of NeuAc was enriched in the nuclear preparation as compared to various other cytosolic and non-cytosolic enzymes.Because newly synthesized NeuAc is channelled into a special pool and used for activation to CMP-NeuAc Ferwerda W, Blok CM, van Rinsum J (1983) Biochem J 216:87–92], these results point to a site of activation of NeuAc to CMP-NeuAc other than the nuclear compartment. This might indicate that the nuclear-localized enzyme, CMP-NeuAc synthase, leaves the nucleus before exerting its action.Abbreviations ManNAc kinase (EC 2.7.1.60) ATP:2-acetamido-2-deoxy-d-mannose 6-phosphotransferase - GlcNAc kinase (EC 2.7.1.59) ATP:2-acetamido-2-deoxy-d-glucose 6-phosphotransferase - NeuAc 9-phosphatase (EC 3.1.3.29) N-acetylneuraminate 9-phosphate phosphohydrolase - CMP-NeuAc synthase (EC 2.7.7.43) CTP:N-acetylneuraminic acid cytidylyltransferase - glucose 6-phosphatase (EC 3.1.3.9) d-glucose 6-phosphate phosphohydrolase - p-nitrophenylphosphatase (EC 3.1.3.1/2) orthophosphoric monoester phosphohydrolase - LDH (EC 1.1.1.27) l-lactate:NAD oxidoreductase - (1-4)-galactsyltransferase (EC 2.4.1.38) -N-acetylglucosaminide (1-4)-galactosyltransferase