Immunoreactive nervous system of specific enolase (14-3-2 protein) in human serum and cerebrospinal fluid

Nervous system-specific 14-3-2 protein is an acidic enolase (EC 4.2.1.11) isoenzyme which is found in high concentrations in nervous tissue and which is also considered to be a molecular marker for amine precursor uptake and decarboxylation (APUD) cells. A radioimmunoassay for this protein shows levels of immunoreactivity of 10 ng/ml and 5 ng/ml in human cerebrospinal fluid and serum respectively. The immunoreactivity in concentrated cerebrospinal fluid dilutes out in parallel with the standard curve in the assay, has a similar molecular weight to the immunoreactivity in soluble protein extracts of whole human brain, and on polyacrylamide gel electrophoresis migrates as two forms representing the homodimer and probably the heterodimer species of the enzyme. The protein also occurs at relatively high levels in erythrocytes and an approximately 1% haemolysis would be sufficient to account for the normal serum level of immunoreactivity. Clinical measurements of 14-3-2 protein in neurological disorders or APUD-system disease could be potentially useful in cerebrospinal fluid but are unlikely to be of value in serum.