Use of mutagenic agents in improvement of α-amylase production by bacillus subtilis

Alpha-amylase immobilized on plastic supports: stabilities, pH and temperature profiles and kinetic parameters

The covalent immobilization of alpha-amylase on new isocyanate, acid chloride and carboxylic acid--activated plastic supports shows the viability of such supports for immobilizing enzymes, especially those reacting with 1,6-diaminohexane and glutaraldehyde for producing side arms. The operational stability of immobilized alpha-amylase could be extended by crosslinking the enzyme or by extending the support's side arm (substrate concentration has no effect). Inactive immobilized alpha-amylase were unfolded and then refolded at elevated temperature, these supports were found to be essential in increasing the stability of the enzyme during refolding. The pH curves for the immobilized enzyme were in general found not to be shifted from the soluble enzyme's pH optimum, although one isocyanate plastic support derivative shifted the pH activity profile of alpha-amylase to a higher range by 1.5 pH units, probably due to reaction between the enzyme and the free anhydride groups existing on the support's surface. In all cases, the immobilized enzyme's temperature activity profiles were shifted to a lower temperature range when compared to the soluble enzyme. The immobilized alpha-amylase Michaelis constants increased and the the maximum rates and specific activities decreased when compared to the soluble enzyme kinetic parameters.

Microbial amylolytic enzymes

Starch-degrading, amylolytic enzymes are widely distributed among microbes. Several activities are required to hydrolyze starch to its glucose units. These enzymes include alpha-amylase, beta-amylase, glucoamylase, alpha-glucosidase, pullulan-degrading enzymes, exoacting enzymes yielding alpha-type endproducts, and cyclodextrin glycosyltransferase. Properties of these enzymes vary and are somewhat linked to the environmental circumstances of the producing organisms. Features of the enzymes, their action patterns, physicochemical properties, occurrence, genetics, and results obtained from cloning of the genes are described. Among all the amylolytic enzymes, the genetics of alpha-amylase in Bacillus subtilis are best known. Alpha-Amylase production in B. subtilis is regulated by several genetic elements, many of which have synergistic effects. Genes encoding enzymes from all the amylolytic enzyme groups dealt with here have been cloned, and the sequences have been found to contain some highly conserved regions thought to be essential for their action and/or structure. Glucoamylase appears usually in several forms, which seem to be the results of a variety of mechanisms, including heterogeneous glycosylation, limited proteolysis, multiple modes of mRNA splicing, and the presence of several structural genes.

Isolation and characterization of a 2.2-kb operon preceding the alpha-amylase gene of Bacillus amyloliquefaciens

A DNA region of 2.8 X 10(3) base pairs (2.8 kb) upstream of the Bacillus amyloliquefaciens alpha-amylase gene has been isolated. This DNA gave rise to a 2.2-kb transcript. The 3' end of the transcript was mapped with S1 nuclease and shown to terminate 49 base pairs upstream of the -35 region of the alpha-amylase promoter. In B. subtilis minicells this 2.2-kb transcript coded for three different polypeptides, thus indicating a polycistronic operon-type structure. The location and the order of the polypeptides were established using DNA deletions. The joining of the 2.2-kb operon to the downstream alpha-amylase gene in the plasmid pUB110 did not have any significant effect on the level of expression of the alpha-amylase.

Nucleotide sequence of the promoter and NH2-terminal signal peptide region of the alpha-amylase gene from Bacillus amyloliquefaciens

We have isolated and partially sequenced the gene coding for alpha-amylase (EC 3.2.1.1) from Bacillus amyloliquefaciens by molecular cloning in the plasmid pUB110 using Bacillus subtilis as a host. The nucleotide sequence of the NH2-terminal region of the cloned gene was determined and found to contain a 31-residue-long stretch of amino acids preceding the NH2-terminal sequence of the extracellular alpha-amylase. Within this sequence there is a 15-residue-long stretch of uncharged amino acids similar to that found at the NH2 terminus of other precursors to exported proteins. This "signal sequence" is probably removed in conjunction with the translocation of alpha-amylase through the cytoplasmic membrane. In vitro labeling of alpha-amylase with radioactive amino acids in a coupled transcription-translation system followed by partial sequencing established the exact location of the NH2 terminus of the alpha-amylase gene. The nucleotide sequence preceding the NH2 terminus has properties resembling the RNA-polymerase- and ribosome-binding sites found at the 5' terminus of many prokaryotic genes.