An electrophoretic analysis of peptidases was carried out in a population of American mink. Based on substrate and tissue specificities, as well as subunit composition, homologies were established between mink peptidases A, B, C, D and S and human peptidases. Polymorphism for peptidases B and D was demonstrated for minks of three coat colour types. Breeding data indicated that the peptidase variations are under the control of allele pairs at distinct autosomal loci designated as PEPB and PEPD, respectively. Using a panel of American mink-Chinese hamster hybrid clones, the gene for PEPB was assigned to mink chromosome 9.

Erythrocyte glucose-6-phosphate dehydrogenase (G6PD) was examined by 13% starch gel electrophoresis in 74 mules (42 females and 32 males), 35 donkeys, and ten horses. The quantitative expression of the parental alleles at the Gpd locus varies greatly in female mules from the hemizygous expression of the maternal allele to that of the paternal. The data obtained indicate that the X chromosomes are randomly inactivated in females mules. No selective advantage of a cell population with a maternally (or paternally) derived X active was found in female mule erythrocytes. It is suggested that the phenotypic variability in the expression of the parental Gpd alleles is related to the random proportions established between cells having either a maternal or paternal X active in an initiator (stem) cell group giving rise to erythroid tissue. Initiator cell numbers estimated for erythroid tissue (six or seven) are close to those reported for human females and intergeneric fox hybrids. These numbers may vary depending on the duration of the time of determination and the division rate of initiator cells at determination.

The electrophoretic mobilities of 52 enzymes and proteins were used as measures of the genetic similarity between the sibling species Microtus arvalis and M. subarvalis. The two vole species differed in the electrophoretic mobilities of seven (glucose-6-phosphate dehydrogenase, adenylate kinase, diaphorase, lactate dehydrogenase-A, alpha-galactosidase, 6-phosphogluconate dehydrogenase, and hemoglobin) of these markers. This allowed us to accept the seven markers assayed as species-specific markers. Based on the frequency distribution of the genes at the polymorphic loci of M. arvalis and M. subarvalis, the degree of their genetic similarity was estimated as 0.312 and the genetic distance as 1.164 by Nei's formula. The estimates for genetic similarity were close to those obtained for species recognized as distinct.

The functional properties of purified glucose-6-phosphate dehydrogenase (G6PD) from the erythrocytes of Artic foxes (Alopex lagopus) and silver foxes (Vulpes vulpes) were investigated. It was found that pH optima for G6P D range from 8.15 to 8.25 in Arctic foxes and from 10.2 to 10.4 in silver foxes. For G6P, the estimated Km values were 74 X 10(-6) M (at pH 8.2) and 166 X 10(-6) M (at pH 10.2) in Artic foxes and 58 X 10(-6) M (at pH 10.2) and 40 X 10(-6) M (at pH 8.2) in silver foxes. The Km values for NADP were estimated as 62 X 10(-6) M (at pH 8.2) and 86 X 10(-6) M (at pH 10.2) in the Artic foxes and 15 X 10(-6) M (at pH 10.2) and 12 X 10(-6) M (at pH 8.2) in the silver foxes. It was found that Mg2+ ions exert a significant activating effect on G6P D in the Arctic fox and do not affect appreciably its activity in the silver fox. The experimental data indicate that slight differences in the electrophoretic mobility of G6P D are associated with considerable functional differences in this enzyme between the two fox species.

The electrophoretic pattern of glucose-6-phosphate dehydrogenase (G6PD) was studied in 60 intergeneric fox hybrids (Alopex lagopus x Vulpes vulpes), 33 females and 27 males. It is shown that the structural gene for G6PD, designated Gpd, is located on the X chromosome in both Arctic and silver foxes. Analysis of G6PD patterns in the erythrocytes of hybrid females demonstrated that the phenotypic expression of parental alleles at the Gpd locus varied considerably: from 1:1 to the hemizygous manifestation of an allele of either the Artic or the silver fox. The expression of the parental alleles at this locus is different in the various tissues of single female hybrids. It is suggested that the variable quantitative expression of the alleles at the Gpd locus in hybrid females is related to the presence of two cell populations having in an active state either the X chromosome of the Arctic fox or that of the silver fox. It is also proposed that the size of the two cell populations is largely affected by the different relationships between cells having different activated X-chromosomes among initiator (stem) cells from which various definitive organs and tissues develop. The number of initiator cells for erythroid tissue has been calculated to be five or six.