Synthesis of N-acetylneuraminic acid and of CMP-N-acetylneuraminic acid in the rat liver cell.
Adult male rats, under starving and normal conditions, were injected intravenously with N-acetyl[3H]mannosamine and after various time intervals the specific radioactivities of free N-acetylneuraminic acid (NeuAc) and CMP-N-acetylneuraminic acid were determined in the liver. The specific radioactivity of free NeuAc was high even within 20s after injection; the maximum was reached between 7 and 10 min. The specific radioactivity of CMP-NeuAc showed a lag phase of approx. 1 min. Thereafter it increased quickly and rose above the specific radioactivity of free NeuAc, reaching a maximum about 20 min after injection. These results point to a channelling of the newly synthesized NeuAc molecules into a special compartment, from which they are preferentially used by the enzyme CMP-sialic acid synthetase. It is suggested that the cytosolic enzyme N-acetylneuraminic acid 9-phosphate phosphatase is working in concert with the nuclear localized enzyme CMP-N-acetylneuraminic acid synthetase. Incorporation of radioactive sialic acid into sialoglycoproteins in liver occurred 2 min after injection, and after 10 min bound radioactivity began to appear in the circulation, indicating a transport time of 8 min of sialoglycoproteins from the point of attachment of sialic acid to the point of excretion.
D000818:Animals; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid / Q000096:biosynthesis*; D006595:Hexosamines / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D019158:N-Acetylneuraminic Acid; D051381:Rats; D011919:Rats, Inbred Strains; D012794:Sialic Acids / Q000096:biosynthesis*; D012795:Sialoglycoproteins / Q000378:metabolism; D013997:Time Factors
D006595:Hexosamines; D012794:Sialic Acids; D012795:Sialoglycoproteins; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid; D019158:N-Acetylneuraminic Acid; C002022:N-acetylmannosamine