Purification, radioimmunoassay, and distribution of human brain 14-3-2 protein (nervous-system specific enolase) in human tissues.

Human 14-3-2 protein, a nervous-system specific enolase (EC 4.2.1.11) isoenzyme, has been purified from human brain and a sensitive radioimmunoassay has been developed for its detection. A systematic survey of human organs has shown that immunoreactive nervous-system specific enolase is present in all human organs but at levels less than 3% of those found in human brain, with especially low levels in liver, kidney and skeletal muscle, and with the highest levels in adrenal and large intestine. In all organs immunoreactive nervous-system specific enolase occurs in two forms representing the heterodimer and homodimer forms of the enzyme, and in all tissues except brain the heterodimer predominates. The presence of nervous-system specific enolase in other organs is unlikely to be explicable by innervation alone since significant quantities are found in red blood cell haemolysates. Tissues which contain amine precursor uptake and decarboxylation cells, for which the protein has been claimed to be a specific molecular marker, do not contain significantly higher levels of immunoreactive nervous-system specific enolase than other tissues. Both the heterodimer and homodimer forms of the enolase appear to be expressed at low levels in all tissues.