Comparisons of the polypeptide chains of globins

Constant rate of evolution in the antigenicity of glucose 6-phosphate dehydrogenase revealed by the enzyme inhibition method

Rabbit and chicken antisera against pure and impure rat glucose 6-phosphate dehydrogenase (G6PD) samples were prepared, and their inhibition potencies (RIP) were measured against G6PDs from 26 vertebrate and invertebrate species. The results demonstrated that the -logRIP values of antisera against G6PDs from various test species neatly correlate with paleontologically estimated divergence times between rat and the test species. This suggests that the antigenicity of G6PD has evolved at a constant rate. The correlation coefficients were evidently greater with chicken antisera than with rabbit antisera, but did not markedly differ between chicken antisera elicited to pure and impure rat G6PD samples. Based on the data obtained with chicken antisera, it is estimated that lineages which separated 250-300 million years ago differ in their G6PDs by one unit of the -logRIP.

Transitions and transversions in evolutionary descent: an approach to understanding

In this paper I lay a quantitative theoretical groundwork for understanding the proportions of the possible types of base substitutions observed between 12 genes sharing a common ancestor and isolated from extant species. The experimentally observed types of base substitution between two sequenced genes do not give a direct measure of the types of base substitutions that occur during evolutionary descent. However, by use of a statistical assemblage of these observations, we can recover, without the assumption of parsimony, the conditional base substitution probabilities that determine this descent. Three methods - direct count, regression, and informational entropy maximization - are described by which these probabilities can be estimated from experimental data. The methods are complementary in that each is most useful for somewhat different types of experimental data. These methods are used to study the ratio of transversions to transitions during gene divergence. Though this ratio is not constant during divergence, it does approach a stable limiting value that in principle can vary from zero, corresponding to 100% transition differences, to infinity, corresponding to 0% transition differences. In practice the limiting ratio tends to hover around a value of two, which is expected on a random basis. However, base substitution pathways that are very nonrandom also may lead to a limiting ratio of exactly two, so that such a value is not diagnostic for random pathways. The limiting ratio can be directly calculated from a knowledge of the twelve conditional probabilities for each type of base substitution, or from a knowledge of the equilibrium base composition of the DNAs compared. An expression is given for this calculation. Fifteen years ago Jean Derancourt, Andrew Lebor and Emile Zuckerkandl (1967), analyzing the amino acid sequence of globin chains coded by nuclear genes, made the original observation that the proportion of transition differences decreases with increasing evolutionary time. Recently Brown et al. (1982) and Brown and Simpson (1982) have reported a decrease in the observed proportion of transition differences in mitochondrial DNA with increasing evolutionary divergence. The conditions that must be satisfied for this type of behavior to occur at stable base composition and with stable base substitution probabilities are defined. Multiple substitutions per se do not lead to a decrease in transition differences with increasing evolutionary divergence.

[Primary structure of the alpha chain of the major component of goose hemoglobins (Anser anser)]

Utilising the homology between goose alpha chain hemoglobin and chicken, the primary arrangement of the amino acid residues of the alpha chain (major component) of goose hemoglobin is presented. Data were obtained from amino acid analysis of the isolated alpha chain and of tryptic peptides of the chain. Their chemical structure was established by Edman degradation, carboxypeptidase A and B and leucineaminopeptidase digestion.

On some principles governing molecular evolution

THE FOLLOWING FIVE PRINCIPLES WERE DEDUCED FROM THE ACCUMULATED EVIDENCE ON MOLECULAR EVOLUTION AND THEORETICAL CONSIDERATIONS OF THE POPULATION DYNAMICS OF MUTANT SUBSTITUTIONS: (i) for each protein, the rate of evolution in terms of amino acid substitutions is approximately constant/site per year for various lines, as long as the function and tertiary structure of the molecule remain essentially unaltered. (ii) Functionally less important molecules or parts of a molecule evolve (in terms of mutant substitutions) faster than more important ones. (iii) Those mutant substitutions that disrupt less the existing structure and function of a molecule (conservative substitutions) occur more frequently in evolution than more disruptive ones. (iv) Gene duplication must always precede the emergence of a gene having a new function. (v) Selective elimination of definitely deleterious mutants and random fixation of selectively neutral or very slightly deleterious mutants occur far more frequently in evolution than positive Darwinian selection of definitely advantageous mutants.