THE HIGH MALTOSE-PRODUCING ALPHA-AMYLASE OF THE THERMOPHILIC ACTINOMYCETE, THERMOMONOSPORA-CURVATA

The alpha-amylase of Thermomonospora curvata catalyses the formation o f very high levels of maltose from starch (73%, w/w) without the atten dant production of glucose. The enzyme was produced extracellularly in high yield during batch fermentation in a 5-1 fermentor. Purification was achieved by ammonium sulphate fractionation, Superose-12 gel filt ration and DEAE-Sephacel ionexchange chromatography. The enzyme exhibi ted maxima for activity at pH 6.0 and 65-degrees-C, had a relative mol ecular mass of 60900-62000 and an isoelectric point at 6.2. The except ionally high levels of maltose produced and the unique action pattern exhibited on starch and related substrates indicate a very unusual mal togenic system. The predominance of maltose as the final end-product m ay be explained by the participation of reactions other than simple hy drolysis and the preferential cleavage of maltotriose from higher malt ooligosaccharides. The enzyme exhibits very low affinity for maltotrio se (K(m) = 7.7 x 10(-3) M) and its conversion to maltose is achieved b y synthetic followed by hydrolytic events, which result in the very hi gh levels of maltose observed and preclude glucose formation. This sys tem is distinguished from other very high maltose-producing amylases b y virtue of its high temperature maximum, very low affinity for maltot riose and the absence of glucose in the final saccharide mixture.