ABSTRACT
Oxidoreductases are an important family of enzymes that are used in many biotechnological processes. An experimental design was applied to optimize partition and purification of two recombinant oxidoreductases, glucose dehydrogenase (GDH) from Bacillus subtilis and d-galactose dehydrogenase (GalDH) from Pseudomonas fluorescens AK92 in aqueous two-phase systems (ATPS). Response surface methodology (RSM) with a central composite rotatable design (CCRD) was performed to optimize critical factors like polyethylene glycol (PEG) concentration, concentration of salt and pH value. The best partitioning conditions was achieved in an ATPS composed of 12% PEG-6000, 15% K2HPO4 with pH 7.5 at 25°C, which ensured partition coefficient (KE) of 66.6 and 45.7 for GDH and GalDH, respectively. Under these experimental conditions, the activity of GDH and GalDH was 569.5U/ml and 673.7U/ml, respectively. It was found that these enzymes preferentially partitioned into the top PEG-rich phase and appeared as single bands on SDS-PAGE gel. Meanwhile the validity of the response model was confirmed by a good agreement between predicted and experimental results. Collectively, according to the obtained data it can be inferred that the ATPS optimization using RSM approach can be applied for recovery and purification of any enzyme from oxidoreductase family.
Subject(s)
Bacillus subtilis/enzymology , Bacterial Proteins , Galactose Dehydrogenases , Glucose 1-Dehydrogenase , Pseudomonas fluorescens/enzymology , Bacillus subtilis/genetics , Bacterial Proteins/biosynthesis , Bacterial Proteins/chemistry , Bacterial Proteins/genetics , Bacterial Proteins/isolation & purification , Galactose Dehydrogenases/biosynthesis , Galactose Dehydrogenases/chemistry , Galactose Dehydrogenases/genetics , Galactose Dehydrogenases/isolation & purification , Glucose 1-Dehydrogenase/biosynthesis , Glucose 1-Dehydrogenase/chemistry , Glucose 1-Dehydrogenase/genetics , Glucose 1-Dehydrogenase/isolation & purification , Pseudomonas fluorescens/genetics , Recombinant Proteins/biosynthesis , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/isolation & purificationABSTRACT
To investigate the heterologous expression of Pseudomonas genes in Escherichia coli we have cloned P. fluorescens DNA in an E. coli [cosmid] system. A colony bank representing the whole P. fluorescens chromosome was screened immunologically using a modification of the method described by Broome and Gilbert (1978). Radioactive labelling of the antibodies was replaced by conjugation with horseradish peroxidase. Among 523 E. coli colonies one was D-galactose dehydrogenase-positive. The expression of this enzyme in primary clones was lower than in the uninduced Pseudomonas. Subcloning of the D-galactose dehydrogenase gene, in vitro mutagenesis of the DNA, and coupling to a strong E. coli promoter yielded an E. coli strain that produces 90 times more of the enzyme than the induced P. fluorescens.
