Directed assembly of polypeptis of the isozymes of lactate dehydrogenase

Lactate dehydrogenases in Antarctic and temperate fish species

1. The kinetics of lactate dehydrogenase (both forward and back reaction) in cardiac and skeletal muscle of an Antarctic teleost have been compared with a temperate teleost of comparable morphology and ecology. 2. In both species the forward reaction (pyruvate to lactate) is maximally activated at 2.5-4 mM pyruvate and inhibited above this level. 3. The Michaelis constant (Km) for pyruvate is not significantly different between muscle types or between species when measured at their normal environmental temperature. 4. Km for pyruvate varies with temperature in a positive direction. 5. The back reaction (lactate to pyruvate) is maximally activated by 12-16 mM lactate but only in skeletal muscle of the antarctic species is there inhibition above this level. 6. The Km for lactate is significantly (P less than 0.05) lower in the Antarctic fish cardiac muscle. 7. While the two species are morphologically and ecologically similar, differences at the biochemical level are discussed with respect to environmental temperature range and conservation of enzymic characteristics.

Biochemical and genetic properties of oligomeric structures: a general approach

The oligomers constituted by association of different subunits can exist under multiple forms. In the case of the genetically variable proteins, such a multiplicity leads to numerous questions (i) on the enumerations: what is the number of active forms when a given subunit can make the oligomer inactive, or when the subunits are encoded by s alleles; (ii) on the subunit effects on biochemical properties: how to estimate these effects, are they equal, are there interactions between subunits, etc. Theoretical methods for the study of such oligomeric structures are developed, which mainly rely on linear model techniques. Peculiar properties examined are Vmax and Km, but also the quantities of the various oligomers, which depend on their association law. This approach is extended to the oligomers composed of different sets of subunits, as are for example some enzymes. These aspects are discussed from numerous bibliographic examples, with special reference to molecular interactions (protein complementation or molecular heterosis). Otherwise the genetic application of this theoretical approach is presented: it is possible to consider a genotype as an oligomer of alleles, and thus to study their effects and their interactions, in the one-locus case as well as in the several-loci case. The relevance of this generalization is discussed in connection with two other concepts, the "sequence space" used in molecular evolution and the regression of the genotypic values on the number of alleles used in quantitative genetics.

Intracellular mechanisms of the formation of homo- and heteropolymeric isozymes. I. Kinetics of the formation of the heteropolymeric isozyme of malate dehydrogenase in parasexual hybrids of two Acetabularia species

The isozyme pattern of malate dehydrogenase (MDH) of Acetabularia crenulata and A. mediterranea is characterized by heterogeneity in different regions of the cytoplasm of both algae, as well as by species specificity. The formation of the heteropolymeric MDH isozyme is restricted to a definite region of the cytoplasm of heterokaryons and nuclear-cytoplasmic A.crenulata-A.mediteranea hybrids at different stages of their development. The data obtained suggest that the concentrations of the free subunits of MDH, coded for by homologous genes, are unevenly distributed in the cytoplasm of hybrid cells. The heteropolymeric MDH isozyme in these cells is presumably the result of the de novo synthesis of isozyme subunits. This seems plausible inasmuch as no exchange occurs between the homopolymeric MDH isozymes of both parental types in the cytoplasm. The formation of the heteropolymeric MDH isozyme is tentatively related to the spatial compartmentalization of the mRNAs of homologous genes coding for the MDH subunits.

Genetic and molecular analysis of nonrandom dimer assembly of the creatine kinase isozymes of fishes

Species within many families of actinopterygian bony fishes (class Osteichthyes) have a two-banded allelic isozyme phenotype in individuals heterozygous at the creatine kinase A locus. This two-banded pattern is formed by the presence of the two homodimeric isozymes and the absence of the expected heterodimer. Sharks and amphibians have retained the ability to form all three allelic isozymes in individuals which are heterozygous. Reversible denaturation procedures were able to assemble the different allelic CK-A subunits within a species to form CK-A2 heterodimers. Furthermore, heterodimers were formed from different CK-A subunits from highly divergent species after this in vitro molecular hybridization process. It is concluded from these studies that the polypeptide-binding sites of creatine kinase are structurally conservative in most fishes and that the absence of a heterodimer in heterozygous individuals is not due to a structural incompatibility between the different A subunit types or to an instability of the heterodimer during electrophoresis. A temporal and/or spatial isolation of allelic CK-A subunit synthesis and assembly, within differentiated skeletal muscle, appears to have evolved in the actinopterygian bony fishes.

Ontogeny of lactate dehydrogenase isozymes in chicken-quail hybrid embryos

The ontogeny of lactate dehydrogenase (LDH) isozymes was examined in avian hybrids and compared with the isozyme patterns of the parental species. Hybrids were obtained by crossing female Japanese quali (Coturnix coturnix japonica) with male domestic chickens (Gallus gallus domesticus). By use of starch gel electrophoresis and an enzyme-specific stain, traces of embryonic paternally derived LDH were detected in unincubated hybrid eggs. It was concluded that the embryonic genes coding for the B subunits of LDH are activated during the hours between fertilization and oviposition. In early blastoderms, a great excess of maternally stored LDH is present. In the hybrid, the predominantly maternal pattern of isozymes shifts during embryogenesis to a predominantly paternal pattern. This was considered evidence for differential allelic regulation of LDH inactivation. A progressive trend toward the establishment of the adult distribution of isozymes in various tissues was also observed in the hybrid and quail, and found to be similar to chicken LDH isozyme ontogeny.