TheS,X-acetals in nucleoside chemistry. I. The synthesis of 2′- and 5′-O-methylthiomethylribonucleosides

Ribonucleoside 2′- and 5′-O-methylthiomethyl derivatives were synthesized from selectively protected nucleosides by the action of a dimethyl sulfoxide-acetic anhydride-acetic acid mixture.     

Serum esterase genetics in rabbits. IV. The prealbumin and β-globulin systems

Discontinuous starch gel electrophoresis revealed a fourth allele of rabbit prealbumin serum esterase at locus Est-2. This allele is designated Est-2 ^f and appears to be silent. In addition to the prealbumin serum esterases, another serum esterase system was studied in rabbits. This system is localized in the β-globulin region. Genetic analysis indicated that one locus with two codominant alleles controls the variation in this region. Linkage of this system with Est-1 and Est-2 of the prealbumin serum esterases was demonstrated. Comparison of the arrangement of these esterase loci on linkage group VI with the esterase loci on chromosome 8 of the mouse gives additional support for the theory of evolutionary conservation of chromosomal segments coding for mammalian esterases.     

α-Crystallin. The isolation and characterization of distinct macromolecular fractions

alpha-Crystallin was isolated from calf lens periphery by chromatography on DEAE-cellulose and gel filtration. Three distinct populations of macromolecules have been isolated with molecular weights in the ranges approx. 6x10(5)-9x10(5), 0.9x10(6)-4x10(6) and greater than 10x10(6). The concentration of macromolecules at the molecular-weight limits of a population are very low. The members of the different populations do not appear to be in equilibrium with each other. Further, in those molecular-weight fractions investigated, no equilibrium between members of the same population was observed. The population of lowest molecular weight comprises 65-75% of the total material. The amino acid and subunit composition of the different-sized fractions appear very similar, if not identical. The only chemical difference observed between the fractions is the presence of significant amounts of sugar in the higher-molecular-weight fractions. Subunit molecular weights of approx. 19.5x10(3) and 22.5x10(3) were observed for all alpha-crystallin fractions.     

Siderosomal ferritin. The missing link between ferritin and haemosiderin?

A minor electrophoretically fast component was found in ferritin from iron-loaded rat liver in addition to a major electrophoretically slow ferritin similar to that observed in control rats. The electrophoretically fast ferritin showed immunological identity with the slow component, but on electrophoresis in SDS it gave a peptide of 17.3 kDa, in contrast with the electrophoretically slow ferritin, which gave a major band corresponding to the L-subunit (20.7 kDa). Thus the electrophoretically fast ferritin resembles that reported by Massover [(1985) Biochim. Biophys. Acta 829, 377-386] in livers of mice with short-term parenteral iron overload. The electrophoretically fast ferritin had a lower iron content (2000 Fe atoms/molecule) than the electrophoretically slow ferritin (3000 Fe atoms/molecule). Removal and re-incorporation of iron was possible without effect on the electrophoretic mobility of either ferritin species. On subcellular fractionation the electrophoretically fast ferritin was enriched in pellet fractions and was the sole soluble ferritin isolated from iron-laden secondary lysosomes (siderosomes). The amount and relative proportion of the electrophoretically fast species increased with iron loading. Haemosiderin isolated from siderosomes was found to contain a peptide reactive to anti-ferritin serum and corresponding to the 17.3 kDa peptide of the electrophoretically fast ferritin species. Unlike the electrophoretically slow ferritin, the electrophoretically fast ferritin did not become significantly radioactive in a 1 h biosynthetic labelling experiment. We conclude that the minor ferritin is not, as has been suggested for mouse liver ferritin, 'a completely new species of smaller holoferritin that represents a shift in the ferritin phenotype' in response to siderosis, but a precursor of haemosiderin, in agreement with the proposal by Richter [(1984) Lab. Invest. 50, 26-35] concerning siderosomal ferritin.     

Nitrogenase. VIII. M?ssbauer and EPR spectroscopy. The MoFe protein component from Azotobacter vinelandii OP.

We have studied the molybdenum-iron protein (MoFe protein, also known as component I) from Azobacter vinelandi using M?ssbauer spectroscopy and electron paramagnetic resonance on samples enriched with 57Fe. These spectra can be interpreted in terms of two EPR active centers, each of which is reducible by one electron. A total of four different chemical environments of Fe can be discerned. One of them is a cluster of Fe atoms with a net electronic spin of 3/2, one of them is high-spin ferrous iron and the remaining two are iron in a reduced state (probably in clusters). The results are as follows: Chemical analysis yields 11.5 Fe atoms and 12.5 labile sulfur atoms per molybdenum atom; the molecule contains two Mo atoms per 300 000 daltons. The EPR spectrum of the MoFe protein exhibits g values at 4.32, 3.65 and 2.01, associated with the ground state doublet of a S = 3/2 spin system. The spin Hamiltonian H = D(S2/z minus 5/4 + lambda(S2/x minus S2/y)) + gbeta/o S-H fits the experimental data for go = 2.00 and lambda = 0.055. Quantitative analysis of the temperature dependence of the EPR spectrum yields D/k = 7.5 degrees K and 0.91 spins/molybdenum atom, which suggests that the MoFe protein has two EPR active centers. Quantitative evaluation of M?ssbauer spectra shows that approximately 8 iron atoms give rise to one quadrupole doublet; at lower temperatures magnetic spectra, associated with the groud electronic doublet, are observed; at least two magnetically inequivalent sites can be distinguished. Taken together the data suggest that each EPR center contains 4 iron atoms. The EPR and M?ssbauer data can only be reconciled if these iron atoms reside in a spin-coupled (S = 3/2) cluster. Under nitrogen fixing conditions the magnetic M?ssbauer spectra disappeared concurrently with the EPR signal and quadrupole doublets are obserced at all temperatures. The data suggest that each EPR active center is reduced by one electron. The M?ssbauer investigation reveals three other spectral components characteristic of iron nuclei in an environment of integer or zero electronic spin, i.e. they reside in complexes which are "EPR-silent". One of the components (3-4 iron atoms) has M?ssbauer parameters characteristic of the high-spin ferrous iron as in reduced ruberdoxin. However, measurements in strong fields indicate a diamagnetic environment. Another component, representing 9-11 iron atoms, seems to be diamagnetic also. It is suggested that these atoms are incorporated in spin-coupled clusters.     

The tRNA “Wobble Position” Uridines. IV. The Synthesis of 2′-O-Methyl-5-methoxycarbonylmethyluridine and its Derivatives

Abstract

2′-O-Methyl-5-methoxycarbonylmethyluridine (1) was synthesized via N³, 5′, 3′-O-protected intermediate 6. Nucleoside 1 was transformed to the next “wobble uridines”, 2 and 3, by hydrolysis and ammonolysis, respectively.     

The interaction between ADAM22 and 14-3-3β

ADAM family consists of a number of transmembrane proteins that contain a disintegrin and metalloprotease domain. ADAMs are involved in a highly diverse set of biological processes, including fertilization, neurogenesis, myogenesis and inflammatory response. The ADAM proteins have both cell adhesion and protease activities. Adam22 is highly expressed in human brain. The adam22-/- mice presented severe ataxia and died before weaning, but the function of ADAM22 is still unknown. 14-3-3β interacting with ADAM22 was detected by using yeast two-hybrid assay. The specificity of interaction between ADAM22 and 14-3-3β was proved by in vitro binding assay and immunoprecipitation. The major 14-3-3β binding site was located in the last 28 amino acid residues of ADAM22 cytoplasmic tail. Protein 14-3-3β is abundant and plays an important role in mediating cell diffusion, migration and cell cycle control. The interaction of ADAM22 and 14-3-3β suggests that the ADAM22 may play a crucial role in neural function and development.