Chemical and Physical Studies on Rabbit Muscle Enolase

摘要

The end-groups of rabbit muscle enolase were elucidated. Two moles of amino-terminal N-acetylalanine and two moles of carboxy-terminal -lys-ala-lys were found per 82,000 gm of enzyme, thus establishing chemical evidence for two polypeptide chains in the active enzyme. Enolase was found to dissociate in two organic solvent systems. In each case three components were found necessary for rapid dissociation, organic solvent, ammonium sulfate, and versene. Ammonium sulfate was found to dissociate enolase, the sedimentation coefficient decreasing as the salt concentration was increased. A mechanism for the effect of salt on enolase, involving both dissociation and unfolding, was proposed to explain the data. The subunits of enolase in 2 M ammonium sulfate and in the dioxane system were investigated by fluorescence polarization, fluorescence and absorption spectroscopy and optical rotatory dispersion and compared with native enolase. The dimer of enolase was shown to be the active form of this enzyme in dilute solutions. Also, new assay conditions were found which would increase the specific activity from 375 to 570 units per mg. Enolase most probably crystallizes in an inactive form which can readily be converted to the active dimer by dissolving in dilute buffer.