MECHANISMS OF ACTION OF THE ALPHA-AMYLASE OF MICROMONOSPORA-MELANOSPOREA

The alpha-amylase of Micromonospora melanosporea was produced extracel lularly during batch fermentation in a 5.0-1 fermentor. The absence of an organic nitrogen source in its growth medium facilitated subsequen t purification of the enzyme by ammonium sulphate fractionation and tw o consecutive Superose-12 gel-filtration steps. The enzyme exhibited m axima for activity at pH 7.0 and 55-degrees-C and was 72% stable at pH 6.0-12.0 for 30 min at 40-degrees-C. It had a relative molecular mass of 45000 and an isoelectric point at pH 7.6. The enzyme catalyses the conversion of starch to maltose (53%, w/w) as the predominant final e nd-product. Initial hydrolysis of this substrate, however, gave rise t o the formation of maltooligosaccharides in the range maltotriose to m altohexaose. Maximum yields of these intermediate sugars accumulated t o between 31 and 42% (w/w) as the reaction proceeded. The action of th e M. melanosporea amylase on high concentrations of saccharides larger than maltotriose resulted in the formation of mainly maltose and malt otriose without concomitant glucose production. A combination of hydro lytic and transfer events is postulated to be responsible for this phe nomenon and for the high maltose levels achieved.