Purification and Characterization of from Bacillus sp . RK - 1 MaltosePhosphorylase Jsi . st

Baci"us sp. RK-1 was isolated as a bacterium that produced maltose phosphorylase (MPase) in the c"lture supernatant. Screening was done from among about 400 isolates that could grow at 55OC in a medium containing maltose as the sole carbon source. The enzyme was purified to an electrophoretically homogeneous state and some properties were investigated. The Ml of the enzyme was estirnated to be 170 kDa by gel filtration and 88.5 kDa by SDS-PAGE, suggesting that it ¢ onsisted of two identica) subunits. The enzyme showed optimum actiyity around pH 6.0-7.0 and the optimum temperature was about 650C. The enzyme was stable in the range of pH 5.5-・8.0 after keeping it at 4OC for 24 h and retained the activity "p to about 550C after keeping it for 15 mi". This is the first report about an MPase that could be produced in the culture supernatant. Furthermore, these investigations showed that this MPase is one of the most thermostable ones reported so far.