Improved filtration for dye removal using keratin-polyamide blend nanofibrous membranes

Dyes from industrial wastewaters represent one of the most hazardous pollutants as they are not effectively biodegradable. The present work is focused to study the novel properties of keratin-polyamide blend nanofibrous filtration membranes for treating wastewaters containing dye. Keratin protein was extracted from goat hair, a tannery waste through sulphitolysis process. The extracted keratin was blended with polyamide to prepare a nanofibrous membrane through the electrospinning process. The fabricated pristine polyamide and keratin-altered polyamide membranes were characterized and compared for their properties. Effects of solution pH, dye concentration, membrane flux, and membrane capacity have been examined. Very fine nanofibers and enhanced porosity drive the membrane to enhanced flux and higher filtration efficiencies. At pH 2, the dye removal efficiency of the blend membranes was 100, 99, 98, 90, and 83% for 100, 200, 250, 300, and 400 ppm concentrations of dye, respectively. The keratin-polyamide blend membrane exhibited better properties in all aspects. The results of this present investigation indicate that the presence of keratin in filtration membranes is promising for dye removal from the effluents.

Characterization of a structural model of membrane bound cytochrome c-550 from Bacillus subtilis

A structural model of Bacillus subtilis cytochrome c-550 has been built based upon hydropathy analysis, sequence alignment, homology modeling, and energy minimization. The model has a single transmembrane alpha-helix and a water-soluble domain folded around covalently attached heme C. Physical measurements on purified, recombinant cytochrome c-550 have been made to test aspects of the model. Excitation at either 280 or 295 nm yields fluorescence with an emission maximum at 334 nm and a quantum yield of 25% relative to n-acetyltryptophanamide. The model places one (i.e., W115) of the two tryptophans of cytochrome c-550 in the heme domain and the second (i.e., W3) in the transmembrane domain. The indole ring of W115 is within 5 A of the heme macrocycle and is expected to be highly quenched via resonance energy transfer to the heme. In contrast, W3 is at the start of the putative transmembrane helix and could be located a considerable distance from the heme. Förster theory assigns a distance of 42 A from W3 to the heme. This distance is important in adjusting the relative positions of the membrane-spanning and heme-binding domains. Circular dichroism measurements in the ultraviolet region indicate increased alpha-helical content of B. subtilis cytochrome c compared to mitochondrial cytochrome c in support of an alpha-helical transmembrane domain. The ionic strength dependence of redox kinetics for cytochrome c-550 indicates an overall negative charge that is consistent with a calculated pI of 5.4. However, the charge distribution specified by the model indicates a surface for electron exchange that is different from the classical front face used by mitochondrial cytochrome c.

Expression, purification, and characterization of recombinant forms of membrane-bound cytochrome c-550nm from Bacillus subtilis

Bacillus subtilis expresses a cytochrome c-550nm that participates in respiratory electron transfer and is an integral membrane protein. Analysis of the B. subtilis cytochrome c-550nm amino acid sequence predicts a single N-terminal transmembrane helix attached to a water-soluble heme binding domain [C. von Wachenfeldt and L. Hederstedt (1990) J. Biol. Chem. 265, 13939-13948]. We have purified cytochrome c-550nm from wild-type B. subtilis and B. subtilis transformed with the shuttle vector pHP13 containing the gene for B. subtilis cytochrome c-550nm (cccA). In B. subtilis transformed with pHP13/cccA there is better than eightfold more membrane-bound cytochrome c-550nm than in wild-type B. subtilis. The overexpressed cytochrome c-550nm can be purified by chromatography on hydroxylapatite and Q-Sepharose media. A six-histidine tag has been added to the C-terminus of cytochrome c-550nm from B. subtilis as a further aid for purification. This strain produces cytochrome c-550nm to a level fourfold greater than wild type and allows for one-step purification using metal affinity chromatography. UV-Vis spectroscopy detects no change in the heme C spectrum due to the addition of six histidines. Neither form of B. subtilis cytochrome c-550nm is stable in its reduced state in aerated buffer, unless EDTA is added. The two forms, wild-type and his-tagged, of cytochromes c have similar midpoint redox potentials of 195 and 185 mV, respectively, and are equally good substrates for B. subtilis cytochrome c oxidase. We conclude that the addition of the histidine tag eases the purification of cytochrome c-550nm from B. subtilis plasma membranes and that the additional metal binding site does not compromise the stability or functional properties of the protein.