Formation and Hydrolysis of Maltohexaose by an Extracellular Exo-maltohexaohydrolase

A novel maltohexaose-forming ?-amylase from Bacillus caldovelox: patterns and mechanisms of action

“…Interestingly, the pattern of maltoheptaose hydrolysis (Table 2) shows that, apart from the simple reaction forming maltopentaose and maltose, a further reaction producing maltohexaose occurs. This accumulation is independent of glucose formation, regardless of the brevity of digest examined, and must therefore involve some form of transferase or condensation reaction similar to the system described by Robyt and French (1970) and Monma et al (1983). The production of maltopentaose from starch at the expense of maltohexaose and without the production of glucose, may be another example of a transfer or bimolecular hydrolysis reaction, although no higher sugars produced by such a process were detected in this study.…”

“…This preferential cleavage of maltooctaose is identical to that mediated by the a-amylase of T. vulgaris (Sakano et al 1982). However, it is unlike the "shot-gun" multiple cleavage frequencies displayed by porcine pancreatic a-amylase (Robyt and French 1970) or the single cleavage by the amylase of K. pneumoniae (Monma et al 1983), which yields only maltohexaose and maltose. It should be noted that the latter enzyme is an exo-amylase and not an a-amylase.…”

“…This subsequent disappearance of maltohexaose and appearance of maltopentaose was not concomitant with an increase in glucose, which remained at a relatively low and unchanged level throughout the reaction. With the exception of the a-amylase of B. amyloliquefaciens, all the other microbial maltohexaose-forming a-amylases noted to-date , including those from mutated organisms (Monma et al 1983), produce maltohexaose as an initial hydrolytic product, which is then hydrolysed to maltotetraose and maltose. The B. caldovelox enzyme is similar to that produced by B. amyloliquefaciens in its inability to hydrolyse maltohexaose, and unique in its ability to form maltopentaose at the expense of maltohexaose but without forming glucose.…”

“…Studies on the action patterns of porcine pancreatic a-amylase (Robyt and French 1970) and the exo-amylase of K. pneumoniae (Monma et al 1983) have shown that the switch between simple substrate hydrolysis, End-products formed were identified and quantified by HPLC a The maltoheptaose concentration used was 0.02 M b G6 to G1 are maltohexaose to glucose, respectively and substrate condensation followed by hydrolysis, is substrate-concentration dependent. It could therefore be suggested that the high initial maltohexaose levels, inherent in dextrin (DE 42) and rapidly produced during the initial hydrolysis of 1% (w/v) starch, are involved in some form of condensation reaction that is subsequently followed by hydrolysis.…”

“…The Km values for soluble starch and maltoheptaose were 4.68 mg/ml and 2.13 x 10 -2 M, respectively. (Hayashi et al 1988) and a mutant Klebsiella pneumoniae (Monma et al 1983) that produce maltohexaose in yields of 25-40% (w/w). However, with the exception of B. amyloliquefaciens, maltohexaose is only an initial hydrolysis product and is subsequently broken down to smaller saccharides.…”