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The stability of recombinant proteins has become an increasingly important as more protein therapeutics are developed.In this study, the stability of recombinant human interferon gamma was investigated under storage condition for 0-9 months after production time at 4 and 25℃. The evaluation of biological activity, covalent dimerization, deamidation and oxidation of protein was done by cell culture, HPLC and SDS- PAGE. The results showed represents that antiviral activity was not decreased at 4℃ but decreased as temperature increased to 25℃. The inormation rate of deamidated and oxidized forms and covalent dimers at 25℃ was more rapid than 4℃. Therefore, rhIFN-γ has high stability at 4℃ comparing to 25℃.

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Nowadays, biological substances have allocated many applications to themselves in distinct industries. In this field, biological molecules with various potentials have been identified, from which we can refer to bacteriorhodopsin (BR). Bacteriorhodopsin is found in purple membrane of halobacterium salinarum. Due to its stability and various characteristics like possession of properties of a proton pump, bacteriorhodopsin has many applications in different industries. One of the most important industrial and semi-industrial production processes for bacteriorhodopsin is the isolation and purification of the purple membrane. In this investigation, after halobacterium salinarum culture, the purification was done according to the Yucel method. So as to produce bacteriorhodopsin in semi-industrial scale, a modified method was developed by substitution of mechanical approach with enzymatically method to destruction of DNA and uses of osmotic shock instead of dialyze. This method led to decrease of time and isolation cost in comparison to Yucel method. The contamination percentage of the PM was estimated below 5% for both methods. The purification percentages were 67±1% and 68±4% for the modified method and Yucel method, respectively, which is indicating of the equal purification percentage for both methods. Bacteriorhodopsin amount was 8.2±0.4, 8.1±0.6 mg per liter for the improved method and Yucel method, respectively. The enzyme activity assay by Kuyama method indicated that the pH variation was 1 unit with the same BR amount for both methods. Hence, the modified method introduced in this investigation could reduce time and costs of the purification by maintaining the BR characteristics.

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A systematic parasitological examination was carried out on 266 freshwater fish speci-mens, belonging to 11 species, from Northwest of Iran during the period from Summer 2001 to Summer 2002. Twelve parasite species including Diplostomum spathaceum, Al-locreadium isoporum, Ligula intestinalis, Digrama sp., Caryophylleus laticeps, Rhabdocona hellichi, Eustrongylides excisus, Argulus foliaceus, Lamprolegna compacta, Myxobolus musayevi, M. cristatus, and Neoechinorhynchus rutili were isolated and identified. It was concluded that Sander lucioperca, Albornoides bipunctatus, Capoeta capoeta, Carassius carassius and Barbus capito were five new hosts for those parasites in Iranian freshwater fishes. Furthermore, Myxobolus cristatus is recorded for the first time among Iranian freshwater fishes. All the parasites were collected from natural waters, but these rivers form a very important water reservoir in this area and these parasites can injure cultured fishes under certain conditions.