Defect-impurity complexes with high thermal stability in epi-Si n+-p diodes irradiated with MeV electrons

Defect-impurity complexes with high thermal stability which were generated after high temperature annealing of silicon n⁺-p diodes irradiated with 4 MeV electrons at 300 K have been studied by means of deep level transient spectroscopy (DLTS). Such defects are of interest because of their possible application in controlling the carrier lifetime in silicon power devices. The parameters of four deep level traps have been determined and compared with the results of photoluminescence studies on thermal stability of electron-irradiation-induced defects. A donor like trap with an energy level at E_v + 0.39 eV was assigned to a complex incorporating an interstitial carbon atom and two oxygen atoms (C_iO_2i), which gives rise to the P-line (hν = 0.767 eV) in photoluminescence spectra.     

A preclinical study of the effect of the animal polysaccharide chonsurid on reparative osteogenesis of the jaws

Experimental studies making use of morphological and x-ray methods demonstrated that in comparison with control (filling of mandibular bone defects with blood clots) chonsuride, an animal polysaccharide, promoted earlier filling of postoperative bone cavities with connective tissue replacement of this tissue with coarse-fiber bone tissue. Secondary restructuring and mineralization of bone regenerate were enhanced as well.     

The mechanism of the inhibiting effect of a Yersinia pestis protein factor on the hormone-stimulated response of human thrombocytes

Thermostable protein factor (20000 Da) was prepared from Yersinia pestis avirulent strain EV 1290. This protein inhibited the aggregation of human platelets as well as elevation of [Ca2+], induced by different agonist. The action of this protein on platelets is accompanied by elevation of cellular cGMP levels. This factor activated guanylate cyclase suspension of human platelets. The data indicate that this protein factor of Y. pestis may possibly release in circulation during decay of bacteria and can change the physiological activity of human blood cells and contribute to the pathogenesis of plague.     

Formate dehydrogenase in a reversed micelle system: regulation of catalytic activity and oligomeric composition of the enzyme

Formate dehydrogenases from the methylotrophic bacteria Pseudomonas sp. 101 and Mycobacterium vaccae N10 were studied in a system of Aerosol OT reversed micelles in octane. Three peaks of the catalytic activity were found on the plot of activity versus surfactant hydration degree (the size of the micellar inner cavity) which corresponded to functions of the enzyme in various oligomeric forms: monomeric, dimeric, and octameric. Kinetic data were confirmed by results of sedimentation analysis. The enzyme was chemically modified by a bifunctional reagent (dimethyl suberimidate) to obtain a catalytically active non-dissociating dimeric molecule of formate dehydrogenase. In the case of the covalently-linked non-dissociating dimeric enzyme, the peak which corresponded to the monomeric form of the enzyme was found to disappear from the catalytic activity curve.     

Inhibition of penicillin acylase from Escherichia coli by benzylalkylketones and benzylalkylcarbinols

A number of benzylalkylketones and benzylalkylcarbinols have been synthesized as non-hydrolizable substrate analogues of penicillin acylase (EC 3.5.1.11), and their affinity to the enzyme has been studied. The compounds with plane trigonal carbonyl group (ketones) were established to has bind to the enzyme 20-40 times more tightly than their tetrahedral counterparts with a hydroxyl function (carbinols). 4-Oxo-5-phenylpentanoic acid was found to be one of the most potent reversible competitive inhibitors of penicillin acylase with Ki-31 microM.     

The RFC2 gene, encoding the third-largest subunit of the replication factor C complex, is required for an S-phase checkpoint in Saccharomyces cerevisiae

Replication factor C (RF-C), an auxiliary factor for DNA polymerases delta and epsilon, is a multiprotein complex consisting of five different polypeptides. It recognizes a primer on a template DNA, binds to a primer terminus, and helps load proliferating cell nuclear antigen onto the DNA template. The RFC2 gene encodes the third-largest subunit of the RF-C complex. To elucidate the role of this subunit in DNA metabolism, we isolated a thermosensitive mutation (rfc2-1) in the RFC2 gene. It was shown that mutant cells having the rfc2-1 mutation exhibit (i) temperature-sensitive cell growth; (ii) defects in the integrity of chromosomal DNA at restrictive temperatures; (iii) progression through cell cycle without definitive terminal morphology and rapid loss of cell viability at restrictive temperatures; (iv) sensitivity to hydroxyurea, methyl methanesulfonate, and UV light; and (v) increased rate of spontaneous mitotic recombination and chromosome loss. These phenotypes of the mutant suggest that the RFC2 gene product is required not only for chromosomal DNA replication but also for a cell cycle checkpoint. It was also shown that the rfc2-1 mutation is synthetically lethal with either the cdc44-1 or rfc5-1 mutation and that the restrictive temperature of rfc2-1 mutant cells can be lowered by combining either with the cdc2-2 or pol2-11 mutation. Finally, it was shown that the temperature-sensitive cell growth phenotype and checkpoint defect of the rfc2-1 mutation can be suppressed by a multicopy plasmid containing the RFC5 gene. These results suggest that the RFC2 gene product interacts with the CDC44/RFC1 and RFC5 gene products in the RF-C complex and with both DNA polymerases delta and epsilon during chromosomal DNA replication.     

The oxidant and antioxidant systems in patients with stable stenocardia and with a history of small- and large-focus myocardial infarcts

A study was made as well as a comparison of values of the cholesterol (Chs) lipid fractions concentrations, and of those of the lipid peroxidation processes activity (LPP) and the gluthathione antioxidant system (AOS) status in male subjects aged from 45 to 59 years, healthy individuals and patients with stable angina pectoris and myocardial infarction (micro- and macrofocal) during cicatrizing stage (health resort rehabilitation stage). In patients with various forms of IHD total cholesterol is raised as are atherogenic lipoproteins, and atherogenicity index, intensification being noted of LPO along with a considerable decrease in functional potencies of AOS. Similar pattern of changes of LPO and AOS in patients with stable angina pectoris and myocardial infarction (MI) during cicatrization stage certainly warrants correction of these systems not only in acute phase of MI but at the stage of rehabilitation as well.