微生物与生化技术杂志

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Purification, Amino Acid sequencing and Thermostability of an Extracellular Low Molecular Weight Esterase Produced by Bacillus Subtilis NRRL 41270 in Fermentation

Papagianni M and Papamichael EM

Extracellular esterase activity in Bacillus subtilis NRRL 41270 fermentation broths was found to reside in a small protein with a molecular weight less than 10 kDa. Following purification, esterase activity on fluorescein dibutyrate was estimated at 12 U/min/mg proteins. Enzyme saturation was observed at 5 μM substrate concentration. The produced esterase hydrolysed tributyrin. Its specific activity was estimated to be 17.8 μmol acid released/min/mg proteins. The small protein was subjected to size exclusion chromatography, SDS-PAGE and amino acid sequencing. Analysis revealed a sequence of the following amino acid residues: eevaetysfyhitphdystshispapvqffspap, according to which the molecule has 34 amino acid residues and a calculated molecular mass of 3853, which was in accordance with the gel filtration and SDS-PAGE results. Sequence based analysis and use of bioinformatics tools showed no significant similarity with known proteins while revealed a strongly hydrophobic molecule, with a α-helical conformation in the N-terminal, the rest of the molecule being β-sheet-rich. The enzyme appeared to be thermostable with more than 85% of the original activity maintained after 120 h incubation at 60°C. The producer organism and the features of the micro enzyme, suggest the case of a biotechnologically interesting biocatalyst that should be further researched in terms of its stability and production characteristics.