Malt amylases

Chethan, S., Sreerrama, Y. N., and Malleshi, N. G. (2008b). Mode of action of finger millet malt amylases by the millet phenolics. Food Chem. Ill, 187-191. 

A different method was developed for the purification of pancreatic amylase.4 This enzyme differs somewhat in its solubilities and considerably in the conditions governing its activity, from the corresponding enzyme of malt but the purified amylase preparations from the pancreas and from malt are much alike in respect to the chemical properties above mentioned. Pancreatic amylase is much less stable than malt amylase and much more quickly suffers a loss or diminution of enzymic activity in solution, which as in the case of malt amylase appears to be due, at least chiefly, to hydrolysis of the enzyme molecule. 

In addition to quantitative elementary analyses and qualitative reactions in all of which our pancreatic and malt amylase preparations show results typical of protein substances, we have submitted both of these amylase preparations to quantitative analysis with reference to the eight forms of nitrogen determinable by the VanSlyke method with results which show that the enzyme preparations yield all these products of hydrolysis in proportions within the range of variation shown by such typical protein... 

Pancreatic and malt amylases gradually lose their activity in the aqueous dispersions in which they act. As above noted, there is good evidence that this is due to a destructive hydrolysis of the enzyme. The destructive action of water upon enzyme is less pronounced in the presence of substrate, probably because the combination of enzyme with substrate serves to some extent to protect the enzyme from hydrolysis. It is less rapid in solutions of commercial pancreatin and in water extracts of malt than it is in solutions of purified pancreatic and malt amylases, doubtless because of the presence in the former of substances which are products of protein hydrolysis (proteoses, peptones, polypeptids, amino acids) and whose presence therefore tends to retard further protein hydrolysis and thus to protect the enzyme protein from hydrolytic destruction, or at least to diminish the rate at which such deterioration of the enzyme occurs. 

While pancreatic and malt amylases are similar in their protein nature and alike in yielding maltose as the chief end product of their action upon starch, there are some respects in which they present marked differences. Thus the optimum activities of these two enzymes are shown at quite different hydrogen ion concentrations that of pancreatic amylase in a practically neutral solution, pH = 6.9 that of malt amylase at the distinctly acid reaction of pH = 4.411 In an extended series of experiments with malt amylase it was found that the optimum hydrogen ion concentration was the same whether this were reached by the addition of a strong acid, a weak acid, or an acid salt.12... 

Pancreatic amylase is more sensitive than malt amylase both in the sense that it loses its activity much more rapidly when held in aqueous dispersion, and that it is active only within a narrower range of hydrogen ion concentration. When the two amylases are tested in purified condition upon a dispersion of soluble starch at a temperature of 40°, and each in the presence of its optimum concentration of hydrogen ion and of chloride and phosphate, the enzymic activity of the amylase of the pancreas is fully twice that of the amylase of malt, fairly constant quantitative values being shown in numerous preparations of each enzyme made at different times and in several cases from different specimens of the original material. 

The catalytic action of living organisms, or rather of the proteins they contain, had received the beginnings of an explanation with the experiments of Payen and Persoz on malt amylase separation in 1833 and with J. J, Berzelius s catalyst theory in 1835. In 1897 Eduard Buchner demonstrated that a yeast extract could turn sucrose into ethyl alcohol, Fermentation took place without the presence of living organisms through enzymes. In this case zymase was the catalyst. 

After earlier workers had indicated the existence of several amylases in malt, conclusive evidence that the malt amylase is composed of at least two starch-splitting enzymes was furnished by Ohlsson. Both enzymes are capable of attacking starch and glycogen, but their action is very different. One enzyme, termed saccharogenic amylase by Ohls-... 

Malt amylase is a mixture of a- and /8-amylase and has the following action on starch. 

We will discuss first whether there is an absolutely definite limit of action for all amylases. In the case of the action of /5-amylase on starch and on a-dextrins this question seems to be settled, but in the case of the malt a-amylase the answer is less certain. But certainly the action of the malt amylase practically stops at a certain limit. There is, however, almost always a very slow further action. It is possible that this slow saccharification of the limit dextrins is due not to the amylases but to other carbohydrases which have no action on starch but which are capable of attacking products with short chains. Under all circumstances it must be kept in mind that when in an experiment the saccharification for practical purposes has stopped and the limit dextrins have been isolated, this does not necessarily mean that the limit dextrins will not be further attacked by the enzyme used. But the velocity of this action is certainly very small compared with the velocity of the action on starch. Thus, it must be admitted that experiments involving the isolation of the limit dextrins after the action of a certain amylase on starch are in most cases not strictly reproducible. TJie total yield and chain length distribution of limit dextrins may vary, but their general character is not affected. If a limit dextrin produced by a certain amylase is treated with the same enzyme for a very long time, it is very often transformed to another limit dextrin of lower molecular weight with concomi-... 

Limit Dextrins from Barley Starch. In one experiment, barley starch paste was treated with malt extract, in a second experiment with purified malt amylase (Table XVII). The purified enzyme has yielded limit dextrins with chain lengths greater than those given by the malt extract, possibly because certain carbohydrases capable of attacking the limit dextrins have been removed in the purification or because of a lower stability of the purified enzyme. 

Malt amylase has been resolved into a dextrinogen, a-amylase, which at tacks cent ralglucoside linkages in the starch molecule and j3-amylase which splits off maltose units step by step from the ends of the parent molecule. 

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