Subunit interaction: A molecular basis of heterosis

Abstract

Acid phosphatase, a dimeric enzyme, in Drosophila malerkotliana was studied in isogenic flies to explore the molecular basis of heterosis. As the enzyme activity in heterozygotes is 34% more than that in the better parent (S/S), heterosis is indicated. V _max, K _m , and K _i values are 14.60, 3.6×10⁻⁴ m, and 0.45×10⁻⁴ m, respectively, for the enzyme from F/S flies and 11.80, 4.0×10⁻⁴ m, and 0.37×10⁻⁴ m, respectively, for the enzyme from S/S flies. Thus heterosis for enzyme activity results from a better enzyme in F/S flies. The higher efficiency and better quality of the enzyme in F/S flies were traced to the heterodimeric allozyme, present only in heterozygotes. Enzyme activity, V _max, K _m , and K _i values are 0.739, 42.1; 3.6×10⁻⁴ m, and 0.50×10⁻⁴ m, respectively, for the heterodimeric and 0.513, 36.8; 4.1×10⁻⁴ m, and 0.37×10⁻⁴ m, respectively, for the better parental homodimeric allozyme. On an equimolar basis the enzyme activity of the heterodimer is 44% higher than that of the better homodimer. The better performance of the heterodimer is probably a reflection of superior conformation resulting from interaction between component subunits (F and S polypeptides).