Genetically controlled variation in the shapes of enzymes

Gel electrophoresis in studies of protein conformation and folding

Electrophoresis through polyacrylamide gels is a useful method for distinguishing conformational states of proteins and analyzing the thermodynamic and kinetic properties of transitions between conformations. Although the relationship between protein conformation and electrophoretic mobility is quite complex, relative mobilities provide qualitative estimates of compactness. Conformational states which interconvert slowly on the time scale of the electrophoretic separation can often be resolved, and the rates of interconversion can be estimated. If the transitions are more rapid, then the electrophoretic mobility represents the equilibrium distribution of conformations. Protein unfolding transitions induced by urea are readily studied using slab gels containing a gradient of urea concentration perpendicular to the direction of electrophoresis. Protein applied across the top of such a gel migrates in the presence of continuously varying urea concentrations, and a profile of the unfolding transition is generated directly. Transitions induced by other agents could be studied using analogous gradient gels. Electrophoretic methods are especially suited for studying small quantities of protein, and complex mixtures, since the different components can be separated during the electrophoresis.

Rare allele heterozygosity and relative electromorph mutation rates in man

Previous studies of human populations have failed to find a significant relationship between genetic variability, as measured by total heterozygosity, and cistron size, as measured by subunit molecular weight of proteins, but the number of different rare alleles in human populations has been shown to be correlated with subunit size. The present paper examines these relationships further, utilizing data on electrophoretic variants at 27 loci for 12 human populations with a total of 800 000 individual system observation. The results indicate that, if genetic variability is measured by rare allele heterozygosity instead of total heterozygosity, there is a significant correlation with subunit size. In addition, there are significant differences for rare allele heterozygosity between multimeric and monomeric proteins, the range of variability being less in the multimers (and in the total) than for monomers. Finally, rare allele heterozygosity has a much bigger range of variability than the range of subunit size. By contrast, the range of rare allele heterozygosity between populations is less than ten-fold, a factor not evident in effective population sizes. Both interlocus and interpopulational estimates of relative electromorph mutation rates (REMR) have been calculated, utilizing the distributions of the number of different rare alleles as well as rare allele heterozygosity. The range of these estimates are much lower than the estimates given by Zouros (1979) using total heterozygosity as input.

Polyploidy, plants, and electrophoresis

Investigations of polyploidy using electrophoresis are at present severely limited by several areas of difficulty which limit all applications of this technique. The technical problems inherent in electrophoresis of plants, namely extraction of active extracts and maximizing resolution of electrophoretic variants through investigation of gel and especially assay conditions, have never been addressed explicitly. No rationale for initiating work on a new species is available. Analytical approaches to defining the conditions which limit resolution are rare. Gel-to-gel variation is poorly controlled, seldom monitored. The individual nature of electrophoretic investigations limits the comparability of data among labs. In short, "hit-and-miss" approaches predominate, and these limit investigation. Techniques are now available which one can hope will greatly improve the experimental situation.