Naturally occurring enzyme activity variation in Drosophila melanogaster. II. Relationships among enzymes.

This report describes an investigation of the specificities of the genetic effects, caused by whole chromosome substitution, on the activities of 23 enzymes in Drosophila melanogaster. Two types of correlation estimates are examined, the product-moment correlation over the chromosome substitution line means and the corresponding correlation of line effects, which is a standardized covariance component estimate. The two types of correlations give very similar results. Although there is ample evidence for specific line effects on individual enzyme activities, there are extensive intercorrelations among many of the enzymes for both second- and third-chromosome substitution lines. The pattern of correlations with respect to the metabolic functions or other properties of the enzymes is difficult to visualize by inspection of the correlation matrix, so a multivariate graphical technique, the biplot (GABRIEL 1971), was employed to obtain a two-dimensional view of relationships among the enzyme activities. The second and third chromosome lines show similar patterns. Four of the five mitochondrial enzymes form one highly intercorrelated group whereas another highly intercorrelated group contains several cytosolic enzymes. Within the cytosolic group, particularly high correlations are observed between enzymes that have glucose 6-phosphate as a substrate or product and between enzymes that are NADP-dependent. Although the pattern of intercorrelations is not clearly explicable in terms of metabolic relationships among the enzymes, there is some tendency for enzymes that catalyze sequential reactions or share a substrate or product to have correlated activity levels.