The increased negative charge of prealbumin in cerebrospinal fluid is acquiredin vitroby oxidation of the cysteinyl residues without formation of disulphides

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Abstract
The reported charge difference between prealbumin (PA) in cerebrospinal fluid (CSF) and PA in plasma has been traced to the cysteinyl residues. In freshly drawn CSF and plasma, PA had the same electrophoretic mobility at pH 8.6 and the same microheterogeneity by electrofocusing under denaturing and non-denaturing conditions. No differences in molecular weight were detected on sodium dodecyl sulphate polyacrylamide slab gel electrophoresis between PA isolated from stored CSF and PA isolated from serum. In fresh samples of CSF and plasma almost all half-cystine residues of PA reacted with 5, 5′-dithio bis (2-nitrobenzoic acid) (DTNB). During storage of CSF and plasma the single cys-10 in the PA subunits acquired an extra negative charge and became unreactive towards DTNB due to oxidation mainly without formation of disulphides. This reaction proceeded faster in CSF than in plasma and explains the reported lower isoelectric pH and the higher electrophoretic mobility of PA in CSF compared to the corresponding plasma.