Reactive species or free radicals include reactive oxygen and nitrogen species that are called reactive oxygen nitrogen species. Reactive oxygen species are formed as a natural by-product of the normal metabolism of oxygen and have significant roles in cell signaling and homeostasis. The reactive oxygen species are generated as a byproduct of biochemical reactions, in mitochondria, peroxisomes, cytochrome P , and other cellular components. When oxygen homeostasis is not maintained, oxidative stress is increased in the cellular environment. Superoxide, hydrogen peroxide and hydroxyl radicals are normal metabolic by-products which are generated continuously by the mitochondria in growing cells. Microsomal cytochrome P enzymes, flavoprotein oxidases and peroxisomal enzymes are other significant intracellular sources of reactive oxygen species.

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Major B-cell epitopes are located at the major hydrophilic region (MHR) of hepatitis B virus (HBV) surface antigen (HBsAg). The genotypes, subtypes, and naturally occurring amino acid (aa) substitutions of MHR were analyzed in 81 Turkish adult patients (41 inactive HBsAg carriers and 40 patients with chronic hepatitis B) by direct sequencing of the S gene fragment. All the isolates were genotype D according to the phylogenetic analysis. The most common HBsAg subtype was ayw2, followed by ayw3 while one isolate specified ayw4 by encoding Leu127. MHR variants were detected in 22 of the 81 (27.2%) isolates. The prevalence was significantly higher in the chronic hepatitis B group (42.5%) compared to inactive HBsAg carriers (12.2%). Twenty-two samples had a total of 26 amino acid substitutions involving 14 positions. The majority of the patients had a single variation. Most of the amino acid substitutions were located at the HBs1 region of the MHR, while 9 of the 26 were in the classic "a" determinant (aa 124-147). When samples with "a" variants were evaluated by two different commercial HBsAg tests, only the isolate with Ser143Leu variation had a decreased reactivity in the assay using monoclonal antibodies for capture and detection. In conclusion, the findings of the study was in accordance with previous studies showing HBV genotype and subtype homogeneity (genotype D/ayw) in Turkey. Naturally occurring MHR and "a" determinant variants were common, especially among chronic hepatitis B patients. The influence of detected "a" variants on diagnostic assays was limited.

A novel ␤-lactamase gene was cloned from the whole-cell DNA of an enterobacterial Citrobacter gillenii reference strain that displayed a weak narrow-spectrum ␤-lactam-resistant phenotype and was expressed in Escherichia coli. It encoded a clavulanic acid-inhibited Ambler class A ␤-lactamase, GIL-1, with a pI value of 7.5 and a molecular mass of ca. 29 kDa. GIL-1 had the highest percent amino acid sequence identity with TEM-1 and SHV-1, 77%, and 67%, respectively, and only 46%, 31%, and 32% amino acid sequence identity with CKO-1 (C. koseri), CdiA1 (C. diversus), and SED-1 (C. sedlaki), respectively. The substrate profile of the purified GIL-1 was similar to that of ␤-lactamases TEM-1 and SHV-1. The bla GIL-1 gene was chromosomally located, as revealed by I-CeuI experiments, and was constitutively expressed at a low level in C. gillenii. No gene homologous to the regulatory ampR genes of chromosomal class C ␤-lactamases was found upstream of the bla GIL-1 gene, which fits the noninducibility of ␤-lactamase expression in C. gillenii. Rapid amplification of DNA 5 ends analysis of the promoter region revealed putative promoter sequences that diverge from what has been identified as the consensus sequence in E. coli. The bla GIL-1 gene was part of a 5.5-kb DNA fragment bracketed by a 9-bp duplication and inserted between the D-lactate dehydrogenase gene and the ydbH genes; this DNA fragment was absent in other Citrobacter species. This work further illustrates the heterogeneity of ␤-lactamases in Citrobacter spp., which may indicate that the variability of Citrobacter species is greater than expected.