Establishment and Evaluation of a Radioimmunoassay for Neuron-Specific Enolase

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Abstract
Neuron-specific enolase (NSE) was purified from human brain to a specific activity of 91 U/mg with no demonstrable impurities. The enzyme has a molecular weight of 96,000, consists of two subunits of 47,000, and has an isoelectric point at pH 4.5. A radioimmunoassay based on antibody raised in sheep was established. The assay has a sensitivity of 2 μg/l, and an interassay coefficient of variation of 6.4% at 10 μg/l. The reference limit was defined as 10 μg/l, as found in sera from a population of 389 persons. Of 50 untreated patients with small cell lung cancer (SCLC), 70% had NSE levels above 10 μg/l. None of 170 patients with non-SCLC neoplasms had elevated enzyme levels.