Maltose-producing enzymes

The need for maltose-producing enzymes with more appropriate industrial properties has been met by other sources. The enzyme from Bacillus circulans is a p-amylase but exhibits some characteristics that distinguish it from other bacterial -amylases (20). The enzyme is active at 60 C and is much less susceptible to p-chloromercuribenzoate than plant (-amylases. Activity is optimal around pH 7. 

The beta-amylases (EC3.2.1.2) used are enzymes of barley and yeast that act on the non-reducing ends of starch molecules and produce maltose in the beta form from the starch polymers. These enzymes are used to produce high-maltose syrups. Although beta-amylase converts linear chains completely to maltose, the enzyme cannot cleave branch points and the yield of maltose from amylopectin11 (see Chapter 7) is only 55% of the molecule. 

An a-maltose-producing amylase has been described recently by Takasaki (21) originating from a strain of B. megaterium. This enzyme has all the properties of (-amylase (inhibition by sulphydryl agents such as mercuric chloride and p-chloromercuribenzoate with reactivation by cysteine) but produces maltose that is exclusively in the a-anomeric form. It may be that previous "(-amylases" described from this bacterium (9,10,23) are in fact of this type. The pH and temperature optima (7.0 and around 60 0 do not make this enzyme particularly attractive to industry. Novo Nordisk a/s manufactures an exo-attacking, a-amylase that produces maltose in the a-configuration from dextrins. This enzyme is derived from a thermophilic Bacillus strain (22) and is considerably more thermostable than the mesophilic Bacillus (-amylases. 

Diastase or amylase is formed when malt is produced by the germination of barley grains. Malt is therefore a good source of the enzyme. Diastase is also secreted by the salivary glands (when it is known as ptyalin), and also by the pancreas. Its function is to hydrolysef starch to a mixture of maltose and dextrin ... 

Com symps [8029-43 ] (glucose symp, starch symp) are concentrated solutions of partially hydrolyzed starch containing dextrose, maltose, and higher molecular weight saccharides. In the United States, com symps are produced from com starch by acid and enzyme processes. Other starch sources such as wheat, rice, potato, and tapioca are used elsewhere depending on avadabiHty. Symps are generally sold in the form of viscous Hquid products and vary in physical properties, eg, viscosity, humectancy, hygroscopicity, sweetness, and fermentabiHty. 

Amylase operates exclusively on nonreducing, terminal units in amylose or on the branches in amylopectin, to produce maltose directly, and its hydrolytic action on 4 — 1-a-D linkages is stopped by any branch points. Enzyme action is greatly impeded by secondary valence forces, as retro-gradation, for example, is accompanied by an increased resistance to j8-amylolysis.19 The enzyme can be crystallized relatively easily. The mode... 

B-chains until they are acted on by R-enzyme, when maltose or malto-triose will be produced from the residual A-chain, and linear dextrins from the B-chains. The amount of maltose or maltotriose liberated on treating the /3-limit dextrin with R-enzyme will be a measure of the number of A-chains in the molecule, and from these data, the ratio of A B chains in the molecule can be calculated.220 Peat concluded that multiple branching is an intrinsic part of the amylopectin structure, as the observed yield of these sugars was greater than expected for a singly-branched structure. It should be noted that glycogen has been shown by similar enzymic methods to possess a truly random structure.221... 

The enzyme was examined by Fischer following earlier studies by Bour-quelot (39) in France. Bourquelot (39) reported that he had made known in 1883 that an extract from a culture of A. niger hydrolyzed maltose. He now provided evidence that the solution also caused hydrolysis of trehalose. However, since this activity was lost on heating to 63 °C but that responsible for the hydrolysis of maltose was maintained up to 75 °C, he concluded that the fungus produced two different ferments —one a maltase, the other a trehalase. 

This enzyme [EC 2.4.1.8] catalyzes the reaction of maltose with orthophosphate to produce D-glucose and /3-r>-glucose 1-phosphate. 

Enzymes are also added to catalyze the hydrolysis or saccharification of starch. Malt produced by the germination of barley grain contains the enzymes that catalyze this hydrolysis. Sometimes called diastase, the enzymes are primarily a- and 6-amylase. Glucoamylase is a pure enzyme that can now be used. Both diastase and glucoamylase hydrolyze starch polysaccharide to the disaccharide, maltose. For fuel grade ethanol production, hydrolysis takes place at temperatures ranging from about 120°F to 140°F (50°C to 60°C) for about 1 hour. The final product of hydrolysis is called a wort. Solids can be filtered from the wort before continuing. 

Prior to fermentation, the wort is then cooled to temperatures below 85°F (30°C), and the pH is adjusted to about 5. Yeast such as Saccharomyces cerevisiae, Saccharomyces carlsbergensis or Candida brassicae are added and fermentation proceeds for 2 to 3 days under batch processing conditions. Yeast produces the enzymes maltase, zymase, and invertase. Maltase converts maltose to glucose. Zymase converts glucose to ethanol. Invertase converts any sucrose present to fermentable sugar. The following equations illustrate the enzymatic conversion of starch to ethanol ... 

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