Studies of S-adenosylhomocysteine-hydrolase polymorphism in a Croatian population.

Recently, a proven case of human S-adenosylhomocysteine-hydrolase (SAHH) deficiency was reported in a Croatian boy. As molecular analysis of the SAHH gene in this case revealed two different mutant alleles, we investigated the polymorphism of human SAHH in a total of 237 red blood samples from unrelated Croats using starch gel electrophoresis and an enzyme-specific staining procedure. From the relative enzymatic activity of SAHH--determined by densitometric assessment of electrophoretic patterns, and calculated on the basis of the protein concentration of the red blood cells-we detected three individuals as being heterozygous for an SAHH 0-allele. Moreover, a total of four different electromorphic SAHHs have been observed, giving allele frequencies calculated as SAHH 1 = 0.941, SAHH 2 = 0.032, SAHH 3 = 0.006, SAHH 4 = 0.015, and SAHH 0 = 0.006.

High genetic variability of esterase loci in natural populations of Parus major, P. caeruleus, and P. ater.

In Parus major, P. caeruleus, and P. ater the genetic variation of 16 isozyme loci was determined. The focus was on esterases that show high phenotypic variation in natural populations of these species. The degree of heterozygosity of the "non-esterase" loci was 0.029 +/- 0.008 (P. major); 0.023 +/- 0.012 (P. caeruleus), and 0.034 +/- 0.034 (P. ater). Including the esterase loci with up to six alleles per locus the overall degree of heterozygosity increased to 0.130 +/- 0.056 (P. major); 0.143 +/- 0.067 (P. caeruleus), and 0.194 +/- 0.090 (P. ater). We explain the high level of variability of esterases by gene amplification and subsequent selection for high allelic heterogeneity. Substrate specificity of loci is assumed to allow for multiple resistance against various toxic components. Large allelic valiation of esterases, therefore, increases the fitness of Parus species and allows for utilizing new food resources.

Characterization of glycine N-methyltransferase from rabbit liver.

The enzymatic properties of glycine N-methyltransferase from rabbit liver and the effects of endogenous adenosine nucleosides, nucleotides and methyltransferase inhibitors were investigated using a photometrical assay to detect sarcosine with o-dianisidine as a dye. After isolation and purification the denatured enzyme showed a two-banded pattern by SDS-PAGE. The enzyme was highly specific for its substrates with a pH-optimum at pH 8.6. Glycine N-methyltransferase exhibits Michaelis-Menten kinetics for its substrates, S-adenosylmethionine and glycine, respectively. The apparent Km and Vmax values were determined for both the substrates, the other substrate being present at saturating concentrations. The enzyme was strongly inhibited in the presence of S-adenosylhomocysteine, 3-deazaadenosine, and 5'-S-isobutylthio-5'-deoxyadenosine. All other inhibitors investigated, adenosine, 2'-deoxyadenosine, aciclovir, and 5'-N-ethylcarboxamidoadenosine were poor inhibitors of the methylation reaction. Adenine nucleotides and vidarabin were without effect on the enzymatic activity. Based on the kinetic data glycine N-methyltransferase from rabbit liver exhibits appreciable activity at physiological S-adenosylmethionine and S-adenosylhomocysteine levels.

Sex-specific recombination rates in Parus major and P. caeruleus, an exception to Huxley's rule.

Huxley's rule predicts lower recombination rates in the heterogametic sex than in the homogametic one. The genotyping of Parus major and P. caeruleus families at 8 microsatellite and 4 enzyme loci yielded contradicting data. Significant genotypic disequilibrium was observed between esterase-1, esterase-2 and esterase-3 in adults of P. major and between esterase-2/esterase-3 and esterase-2/microsatellite PK-12 in P. caeruleus. Support comes from linkage analyses of nuclear families. In P. major, the recombination rate of esterase-2/esterase -3 in males is significantly lower than in females (theta(male) = 0.076, theta(female) = 0.145). The opposite is found for the recombination rates of esterase-1/esterase-2 and esterase-2/esterase-3 in P. caeruleus (EST-1/EST-2: theta(female) = 0.218, theta(male) = 0.5, EST-2/EST-3: theta(female) = 0.109, theta(male) = 0.194). We conclude that the basis of differences in recombination rates cannot be heterogamety, per se, but must have multiple genetic causes including chromosomal rearrangments that have evolved after the cladogenesis of the two species.