In vitro renaturation of recombinant human pro-urokinase expressed in Escherichia coli.

OBJECTIVE: Recombinant human pro-urokinase forms insoluble inclusion body when overexpressed in Escherichia coli. It must be denatured and renatured in vitro so that it can acquire activity. This study aimed at increasing the renaturation yield of denaturant pro-urokinase. METHODS: We evaluated the basic renaturation conditions of pro-urokinase through qualitative and quantitative analysis of pH, temperature, denatured concentration, protein concentration, and the ratio of reduced and oxidized thiol reagents. We also compared the effects of nonspecific additives, step-wise dilution and urea gradient dialysis. RESULTS: We defined the optimal conditions of pro-urokinase renaturation with a yield of about 20%-30%. CONCLUSION: Different recombinant denatured proteins have different renaturation conditions due to their different molecular sizes, molecular constructions, disulfide bond numbers, and hydrophobicity. The renaturation yield can be increased by optimizing the renaturation conditions of a specific protein.

Rapid and simple method for the most-probable-number estimation of arsenic-reducing bacteria.

A rapid and simple most-probable-number (MPN) procedure for the enumeration of dissimilatory arsenic-reducing bacteria (DARB) is presented. The method is based on the specific detection of arsenite, the end product of anaerobic arsenate respiration, by a precipitation reaction with sulfide. After 4 weeks of incubation, the medium for the MPN method is acidified to pH 6 and sulfide is added to a final concentration of about 1 mM. The brightly yellow arsenic trisulfide precipitates immediately and can easily be scored at arsenite concentrations as low as 0.05 mM. Abiotic reduction of arsenate upon sulfide addition, which could yield false positives, apparently produces a soluble As-S intermediate, which does not precipitate until about 1 h after sulfide addition. Using the new MPN method, population estimates of pure cultures of DARB were similar to direct cell counts. MPNs of environmental water and sediment samples yielded DARB numbers between 10(1) and 10(5) cells per ml or gram (dry weight), respectively. Poisoned and sterilized controls showed that potential abiotic reductants in environmental samples did not interfere with the MPN estimates. A major advantage is that the assay can be easily scaled to a microtiter plate format, enabling analysis of large numbers of samples by use of multichannel pipettors. Overall, the MPN method provides a rapid and simple means for estimating population sizes of DARB, a diverse group of organisms for which no comprehensive molecular markers have been developed yet.

Plasminogen activator inhibitor-1 fused with erythropoietin (EPO) mimetic peptide (EMP) enhances the EPO activity of EMP.

Erythropoietin (EPO) mimetic peptide (EMP) encoding sequence was inserted into the gene of plasminogen activator inhibitor-1 (PAI-1) between Ala348 and Pro349 (P2'-P3'), generating a novel gene, PAI-1/EMP (PMP). This was cloned into pET32a expression vector, fused with TrxA peptide in the vector, and a 63-kDa protein was expressed in inclusion bodies with an expression level >50%. The TrxA/PMP protein was purified by Ni-NTA-agarose metal-ligand affinity chromatography to a purity >90%, showing a single, silver-stained band on SDS-PAGE. Using a reticulocyte counting assay, the EPO activity of PMP was determined to be 5,000 IU/mg, 2,500-fold that of EMP.

Ammonium removal by the oxygen-limited autotrophic nitrification-denitrification system

The present lab-scale research reveals the potential of implementation of an oxygen-limited autotrophic nitrification-denitrification (OLAND) system with normal nitrifying sludge as the biocatalyst for the removal of nitrogen from nitrogen-rich wastewater in one step. In a sequential batch reactor, synthetic wastewater containing 1 g of NH4+-N liter-1 and minerals was treated. Oxygen supply to the reactor was double-controlled with a pH controller and a timer. At a volumetric loading rate (Bv) of 0. 13 g of NH4+-N liter-1 day-1, about 22% of the fed NH4+-N was converted to NO2--N or NO3--N, 38% remained as NH4+-N, and the other 40% was removed mainly as N2. The specific removal rate of nitrogen was on the order of 50 mg of N liter-1 day-1, corresponding to 16 mg of N g of volatile suspended solids-1 day-1. The microorganisms which catalyzed the OLAND process are assumed to be normal nitrifiers dominated by ammonium oxidizers. The loss of nitrogen in the OLAND system is presumed to occur via the oxidation of NH4+ to N2 with NO2- as the electron acceptor. Hydroxylamine stimulated the removal of NH4+ and NO2-. Hydroxylamine oxidoreductase (HAO) or an HAO-related enzyme might be responsible for the loss of nitrogen.

Mutation of Arg154 to Gly154 in urokinase augments its fibrin-specificity.

Rscu-PA and its mutant constructed by in vitro site specific mutagenesis of Arg154 in rscu-PA to Gly154 (mscu-PA) were both expressed in Escherichia coli. After in vitro denaturation and renaturation, the rscu-PA and mscu-PA were purified to homogeneity by Zn2+ selective precipitation, anti-u-PA IgG-sepharose CL 4B affinity chromatography. After activation by plasmin, the kinetic constants for the resultant mtcu-PA against synthetic substrate S2444 hydrolysis were found to be essentially identical to rtcu-PA, suggesting that no impairment had been exerted on the catalytic active site of mtcu-PA. However, both 125I-fibrin plasma-clot lysis and fibrinogenolysis showed that mtcu-PA possessed a higher fibrinolytic activity but hardly any degradation of fibrinogen in plasma compared to rtcu-PA and rscu-PA. It was concluded that the substitution of Arg154 by Gly154 in tcu-PA promoted the fibrin-specificity of urokinase.