Amylase limiting substrate

When the substrate was amylopectin (3-amylase limit dextrin, a different pattern of products was formed, namely Gl, G2 and G3, with no G6, G7 or higher sized dex-trins.14 Reaction with the (3-limit dextrin indicated that Gl, G2 and G3 are formed from the chains between the o-( 1 —6) branch linkages as the outer chains were removed by the action of (3-amylase (see Section 7.2 for a discussion of the action of (3-amylase). It further indicated that G6 and G7 from amylopectin were formed exclusively from longer unbranched outer chains. It also indicated that the number of glucosyl units between the branch linkages of amylopectin were sufficiently few that they could not yield the larger G6 and G7 products, but could give the smaller Gl, G2 and G3 products. 

Fig. 4.—Composition of Corn-starch Hydrolyzates Prepared by Acid Catalysis (Curve a and b), and Idealizations of Compositions Attained by Action of Fungal Amylase on 50 d.e. Acid Hydrolyzate (Curve c and d), by Action of beta-Amylase on 20 d.e. Acid Hydrolyzate (Curve e and f), by Limited Action of beta-Amylase on a low d.e., aif)/ia-Amylase-liquefied Substrate (Curve g and h), and by Further Action of Fungal Amylase or Mixtures of beta-Amylase and Glucoamylase (Curve h and i). [A = 100% maltose, B = 100% D-glucose, C = 100% saccharides other than maltose or D-glucose, or both.]...

The observed rate of production R is equal to the formation rate minus the enzyme decay rate, where X is biomass concentration, S is the concentration of the limiting substrate, E is the activity of the enz3rme, jj is the specific growth rate and K, K, K, Kg are unknown parameters which have to be estimated from experimental data With both a-amylase and proteinase production the cultivation was performed on synthetic media where the concentration of limiting substrate were known and measurable By contrast, in most exocellular enzyme productions complex media with an unknown concentration of unidentified limiting substrates are used The model can be simplified when the mass balance for the limiting substrate S is applied as follows ... 

Fig. 4. Influence of environment as a function of the concentration of the growth limiting substrate (caseinate g/1) for U amylase produced by Bacillus subtilis in batch culture. 

The data19 summarized in Figure 1 show that the extent of the hydrolysis of soluble potato starch by barley beta amylase reaches a limit which is independent of the concentration of the amylase. The data are typical of the action of beta amylases on unfractionated starches, when the hydrolyses are carried out at or near pH 4.5.1 3 6 19 20 Under these conditions, the hydrolysis of unfractionated starches usually ceases when 60 to 64% of the maltose theoretically obtainable from the substrate has been formed. The exact value of the limit obviously will depend upon the concentration of amylopectin in the starch and upon its structure. 

Both processes use starch (com, potato, rice, wheat, etc.) as the substrate. Com and potato starches are most commonly used. In both processes, the starch is hydrolyzed to a dextrose equivalent (DE) of 3 to 8 (see Chapter 21) prior to use.25 If liqui-faction/hydrolysis is not sufficient, retrogradation occurs. This limits the availability of substrate, resulting in low yields of cyclodextrins, and interferes with later recovery steps. If the starch is over-hydrolyzed, the disproportionation reaction dominates and yields of cyclodextrins are low. If an a-amylase is used to hydrolyze the starch, it must be inactivated by acidification, raising the temperature, otherwise, the yield will be greatly reduced. 

Buffered Substrate Solution Disperse 10.0 g (dry-weight basis) of Special Starch in 100 mL of cold water, and slowly pour the mixture into 300 mL of boiling water. Boil and stir for 1 to 2 min, then cool, and add 25 mL of Buffer Solution, followed by all of the /3-Amylase Solution. Quantitatively transfer the mixture into a 500-mL volumetric flask with the aid of water saturated with toluene, dilute to volume with the same solvent, and mix. Store the solution at 30° 2° for not less than 18 h nor more than 72 h before use. (This solution is also known as buffered limit dextrin substrate. )... 

With some natural starches or with glycogen it is possible that the action of the /5-amylase is stopped before all end chains are removed because the substrate molecule has so complicated a network of chains that the enzyme, which presumably has a large molecule, can not penetrate into the inner parts of the substrate molecule. This point has been stressed in the case of glycogen by Meyer and Jeanloz. These authors degraded the substrate by a short treatment with hydrochloric acid to the extent that all end chains were accessible for the enzyme and a true saccharification limit was reached. Experiments with different starches and... 

In addition to their actions on disaccharides, the brush border enzymes further hydrolyze the products of amylase action, including maltose, maltotriose, and a-limit dextrins. The brush border enzymes appear to act in an integrated manner in that there is a flow of substrate from glucoamy-lase and isomaltase to sucrase with the production of the monosaccharides glucose, galactose, and fructose. These monosaccharides are transported into the ehterocyte by... 

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