Structural flexibility of isozyme variants: genetic variants in Drosophila disguised by cofactor and subunit binding.

Wild populations of Drosophila mojavensis exhibit considerable conformational variation in the NAD+-free form of alcohol dehydrogenase (alcohol:NAD+ oxidoreductase; EC 1.1.1.1). The variation appears genetic, as it does not occur within an inbred strain. The NAD+-bound form of alcohol dehydrogenase, present in the same individuals, does not exhibit the variation, suggesting that the binding of NAD+ acts to stabilize conformation. Such cofactor binding to enzymes may thus conceal considerable variation. A similar effect is suggested for binding of esterase subunits.