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Turnover of Free Sialic Acid, CMP‐Sialic Acid, and Bound Sialic Acid In Rat Brain
Author(s) -
Ferwerda Wijnholt,
Blok Corrie M,
Heijlman Jan
Publication year - 1981
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1981.tb00591.x
Subject(s) - sialic acid , biochemistry , chemistry , n acetylneuraminic acid
Adult male rats were injected intraventricularly with N‐[ 3 H]acetylmannosamine. After different time intervals the rats were killed and free sialic acid, CMP‐sialic acid, lipid‐ and protein‐bound sialic acid were isolated from brain and the specific radioactivities determined. Maximal specific radioactivity was reached after approximately 4 h for CMP‐sialic acid, after 10–12 h for free sialic acid and after approximately 42 h for lipid‐and protein‐bound sialic acid. After some days the specific radioactivities of all four pools were the same and decreased equally, with a calculated turnover rate of approximately 3.5 weeks. The conclusion was that this phenomenon was the result of reutilisation of sialic acid and/or precursors. Therefore, the calculated turnover is not the turnover of bound sialic acid, but merely the rate of leakage of sialic acid and/or precursors out of the brain, so that no real turnover can be measured by this method. The first few hours after injection the specific radioactivity of CMP‐sialic acid rose above that of free sialic acid. It is supposed that a compartmentalization exists of free sialic acid. The newly synthesized sialic acid molecules are not secreted into the cytoplasmic pool but are preferentially used for the synthesis of CMP‐sialic acid. The results and conclusions are discussed in view of the general problems concerning turnover measurements of glycoconjugates.