Potato, sweet, beta amylase

Hehre and coworkers showed that beta amylase from sweet potatoes, an inverting, a-specific exo-(l 4)-glucanase, catalyzes the hydrolysis of jS-maltosyl fluoride with complex kinetics which indicated the participation of two substrate molecules in the release of fluoride ion. Furthermore, the reaction was strongly accelerated by the addition of methyl ) -maltoside. Hydrolysis of a-maltosyl fluoride, on the other hand, obeyed Michaelis-Menten kinetics. The main product with both a- and yj-maltosyl fluoride was )S-maltose. The results with )3-maltosyl fluoride were interpreted by the assumption of a glycosylation reaction preceding hydrolysis by which a malto-tetraoside is formed by the replacement of fluoride ion by a second substrate molecule or added methyl -maltoside (see Scheme 5). 

If amylases are to be used as tools for the detailed study of the breakdown and structure of their substrates it is obviously important to separate them from other enzymes and from other naturally associated constituents which may influence the results. It is then equally important to study the properties of the purified amylase and to supply it with the chemical environment necessary to protect it from inactivation and to enable it to act efficiently. With beta amylases this ideal has often been approached. Beta amylases from several sources have been prepared by selective inactivation of other enzymes that accompany them in nature23 and highly active products have been obtained by extensive purification.20 24-26 Balls and his associates have recently reported the crystallization of beta amylase from sweet potato.27... 

The amino acid compositions of the beta-amylase from sweet potato, soya bean, wheat, and malted sorghum have been determined, and are shown in Table XIII. These results may suggest that the beta-amylase from these different sources differs in structure. This is, perhaps, not surprising, but it should be noted that the sorghum amylase contained 9% of pentose, and the important, sulfiir-containing amino acid cysteine was not reported and the soya-bean enzyme still contained traces of aipba-amylase and phosphatase. The sequence of amino acids, or the three-dimensional structure of any... 

Table XIV shows the results of the few reports of the molecular size of beta-amylase. No crystallized enzyme from cereals or beans has yet been examined by physical techniques. There is also a problem regarding the important, sweet-potato enzyme the only full report in the literature has been contradicted, and it has been suggested, without experimental details, that subunits of beta-amylase exist. In addition, in the case of cereal fcefo-amylases, where there is the complication of free and bound enzyme, the wheat and malted-barley enzyme has been reported to contain...

It has been reported that a yellow substance is liberated from crystalline, sweet-potato beta-amylase when the enzyme is subjected to gel filtration on Sephadex at pH 8.8 in the presence of pyrophosphate buffer. The chromophoric material can also be obtained by treating the enzyme with acetic acid, and can readily be reattached. 

Figure 11. Mutarotation of the reaction products formed by the action of various amylases. 0> fhe purified amylase on 2% amylose , the purified amylase on 2% maltohexaose A, sweet potato beta-amylase on 2% amylose and , Bacillus subtilis alpha-amylase on 2% amylose.

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