PURIFICATION AND PHYSICOCHEMICAL PROPERTIES OF AN EXTRA CELLULAR AMYLASE FROM A STRAIN OF BACILLUS AMYLOLIQUEFACIENS ISOLATED FROM DRY ONION POWDER

Enzymatic conversions of starch

This article surveys methods for the enzymatic conversion of starch, involving hydrolases and nonhydrolyzing enzymes, as well as the role of microorganisms producing such enzymes. The sources of the most common enzymes are listed. These starch conversions are also presented in relation to their applications in the food, pharmaceutical, pulp, textile, and other branches of industry. Some sections are devoted to the fermentation of starch to ethanol and other products, and to the production of cyclodextrins, along with the properties of these products. Light is also shed on the enzymes involved in the digestion of starch in human and animal organisms. Enzymatic processes acting on starch are useful in structural studies of the substrates and in understanding the characteristics of digesting enzymes. One section presents the application of enzymes to these problems. The information that is included covers the period from the early 19th century up to 2009.

Directed evolution of a bacterial alpha-amylase: toward enhanced pH-performance and higher specific activity

alpha-Amylases, in particular, microbial alpha-amylases, are widely used in industrial processes such as starch liquefaction and pulp processes, and more recently in detergency. Due to the need for alpha-amylases with high specific activity and activity at alkaline pH, which are critical parameters, for example, for the use in detergents, we have enhanced the alpha-amylase from Bacillus amyloliquefaciens (BAA). The genes coding for the wild-type BAA and the mutants BAA S201N and BAA N297D were subjected to error-prone PCR and gene shuffling. For the screening of mutants we developed a novel, reliable assay suitable for high throughput screening based on the Phadebas assay. One mutant (BAA 42) has an optimal activity at pH 7, corresponding to a shift of one pH unit compared to the wild type. BAA 42 is active over a broader pH range than the wild type, resulting in a 5-fold higher activity at pH 10. In addition, the activity in periplasmic extracts and the specific activity increased 4- and 1.5-fold, respectively. Another mutant (BAA 29) possesses a wild-type-like pH profile but possesses a 40-fold higher activity in periplasmic extracts and a 9-fold higher specific activity. The comparison of the amino acid sequences of these two mutants with other homologous microbial alpha-amylases revealed the mutation of the highly conserved residues W194R, S197P, and A230V. In addition, three further mutations were found K406R, N414S, and E356D, the latter being present in other bacterial alpha-amylases.

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.

Physico-chemical properties of Aspergillus flavus var. columnaris alpha-amylase

The best temperature for the preservation of A. flavus var. columnaris alpha-amylase was -5 degrees C followed by 5 degrees C. CaCl2 at 0.005 M had no effect on the activity in both temperatures. Repeated freezing (-5 degrees C) and thawing followed by freezing (-5 degrees C) had no effect on stability of alpha-amylase. On the other hand, 25 degrees C was the lowest preservation temperature without any effect on the stability on alpha-amylase. 0.005 M CaCl2 decreased the activity of alpha-amylase and reached a 100% inhibition at 35th day. The fungal alpha-amylase had an optimum temperature of 55 degrees C at pH 4.6, but had 60 degrees C in buffer containing 0.005 M CaCl2 and 50 degrees C in buffer containing 0.005 M Na2-EDTA. The addition of 0.01 M CaCl2 greatly increased the thermostability of alpha-amylase at 40, 45, 50, 55 and 60 degrees C for 30 min. Optimum pH for alpha-amylase only was 5, but in the presence of 0.01 M CaCl2 or Na2-EDTA 5.6. The enzyme only was stable for 4 h at 25 degrees C. Whereas addition of 0.01 M CaCl2 showed a loss of 4% compared to a 22% loss in the presence of 0.01 M Na2-EDTA after 4 h at 25 degrees C and 65% loss in the presence of 0.01 M CaCl2 together with 0.01 M Na2-EDTA in the beginning and a 100% loss after 4 h at 25 degrees C. The optimum temperature for the activity of alpha-amylase at pH 5 was 50 degrees C for the enzyme only but 55 degrees C in the presence of 0.01 M CaCl2. However, at pH 6 and 7 optimum temperature was 55 degrees C for the activity of the enzyme only or with 0.01 M CaCl2. The presence of 0.01 M CaCl2 at pH 5, 6 and 7 resulted in increase of enzyme activity at the temperatures above 50, 40 and 25 degrees C, respectively. However, 0.01 M CaCl2 at pH 5 and 6 resulted in decreasing enzyme activity at temperatures below 55 and 45 degrees C, respectively.

Enzymatic degradation of cell wall and related plant polysaccharides

Polysaccharides such as starch, cellulose and other glucans, pectins, xylans, mannans, and fructans are present as major structural and storage materials in plants. These constituents may be degraded and modified by endogenous enzymes during plant growth and development. In plant pathogenesis by microorganisms, extracellular enzymes secreted by infected strains play a major role in plant tissue degradation and invasion of the host. Many of these polysaccharide-degrading enzymes are also produced by microorganisms widely used in industrial enzyme production. Most commerical enzyme preparations contain an array of secondary activities in addition to the one or two principal components which have standardized activities. In the processing of unpurified carbohydrate materials such as cereals, fruits, and tubers, these secondary enzyme activities offer major potential for improving process efficiency. Use of more defined combinations of industrial polysaccharases should allow final control of existing enzyme processes and should also lead to the development of novel enzymatic applications.

Trypsin activation of enterotoxin from Clostridium perfringens type A: fragmentation and some physicochemical properties

Clostridium perfringens type A enterotoxin was activated about 3-fold by treatment with trypsin, without an observed change in molecular weight. On denaturation in 8 M urea, the trypsinated enterotoxin lost a small peptide of about 4000 daltons. The single cysteine residue of enterotoxin was in the small peptide together with seven out of nine residues of proline. Trypsin activation, without removal of the small peptide, increased the 'outside' number of amino groups from eight to eleven. The trypsin treatment of the enterotoxin did not change the antigenic properties of the protein. Glycine was the C-terminal residue of the native enterotoxin while the dansyl alpha-amino acid of the N-terminal could not be identified.