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Chicken brain enolase was found to show multiple forms (I, II and III) separable by DEAE-cellulose column chromatography, whereas enolase from chicken skeletal muscle showed a single form. Brain enolase I, enolase III and muscle enolase were purified to electrophoretic homogeneity. These three isozymes were dimeric enzymes, each being composed of two identical subunits, alpha, gamma and beta, having molecular weight of 51,000 +/- 600, 52,000 +/- 550 and 51,500 +/- 650, respectively, as determined by SDS-polyacrylamide gel electrophoresis analysis. Brain enolases I, II and III and muscle enolase had similar catalytic parameters, including almost the same Km values and pH optima. Specific antibodies against brain enolase I, enolase III and muscle enolase, raised in rabbit, showed no cross-reactivity with each other. Antibodies for brain enolases I and III also reacted with brain enolase II, indicating that brain enolase II was the hybrid form (alpha gamma) of brain enolases I (alpha alpha) and III (gamma gamma). Enolases from chicken liver, kidney and heart reacted with the antisera for brain enolase I, but not with those for brain enolase III or muscle enolase. Developmental changes in enolase isozyme distribution were observed in chicken brain and skeletal muscle. In brain, the alpha gamma and gamma gamma forms were not detected in the early embryonic stage and increased gradually during the development of the brain, whereas the alpha alpha form existed at an almost constant level during development. In skeletal muscle, complete switching from alpha alpha enolase to beta beta was observed during the period around hatching.

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Using chicken brain mRNAs, α and γ enolase precursors were synthesized in the rabbit reticulocyte cell‐free translation system. The product proteins showed molecular weights almost identical to those of the mature subunits. The levels of translatable mRNAs for α and γ subunits were determined by the cell‐free translation system and immuno‐precipitation with specific antisera, during development of chicken brain. The level of α mRNA was high at any developmental stage of the brain. On the other hand, the γ mRNA level was very low at the early embryonic stage, and increased rapidly during development of the brain. These changes were closely correlated with those of the corresponding enzyme activities, indicating that the levels of enolase activities in developing brain were controlled primarily by the level of the translatable α and γ mRNAs.

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