Evolution of acid phosphatase-1 in the genus Drosophila as estimated by subunit hybridization. Interspecific tests.

Abstract

The dimeric enzyme, acid phosphatase-1, was partially purified from eleven species of the genus Drosophila. Dissociated subunits were mixed and allowed to reassociate in forty-one interspecific combinations. In each so-called “quantitative subunit hybridization test”, the relative activities of the heterospecific and the two homospecific enzymes were determined by densitometry. In 34 of the 41 tests significant differences between observed and expected homospecific: heterospecific enzyme activity ratios were detected. The differences ranged from a four-fold excess of the heterospecific enzyme to over a six-fold excess of the homospecific enzymes. In order to measure the enzyme activities on a protein basis, fifteen heterospecific enzymes were purified and used as antigens in CRM tests. The antisera were diluted such that only the homologous subunit in the heterospecific enzyme complexed the acid phosphatase antibodies. The results from each CRM test show that the heterospecific enzymes is only one-half as antigenic as the homologous homospecific enzyme, when the two are adjusted to equal catalytic activities. Thus, the differences between observed and expected levels of acid phosphatase activity measured by the quantative subunit hybridization technique apparently reflect differences in the relative amounts of protein which form during subunit reassociation. The technique, then, appears to detect differences in acid phosphatase subunit affinities.