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Production of extracellular alpha-glucosidase was studied with strain KP 1006 of a new species of thermophilic Bacillus, which was isolated from soil samples by enrichment at 65 C. alpha-Glucosidase production was maximum at 60 C and at an initial pH of 6.5. The final enzyme yield was increased by starch, maltose, glycerol, peptone, and yeast extract but reduced by acetate and gluconate, alpha-Glucosidase was formed in the cytoplasm and accumulated as a large pool during the logarithmic growth phase. At a midpoint of this period, the enzyme appeared in the culture broth, and its level increased until the end of the stationary phase.

A p-nitrophenyl-alpha-D-glucopyranoside-hydrolyzing alpha-glucosidase from an obligate thermophile, Bacillus thermoglucosidius KP 1006, gave a triphasic relationship at pH 6.8 in the van't Hoff plot of Km, in the Arrhenius plot of the first order rate constant of inactivation with 0.1% sodium dodecyl sulfate, and in the logarithmic plot of the maximal fluorescence intensity at 346 nm versus reciprocal of temperature. The respective plots exhibited two breaks at 40 and 61 degrees C, 43 and 62 degrees C, and 40 and 61 degrees C. However, the Arrhenius plot of the molecular activity at pH 6.8 had a single discontinuity at 64 degrees C. These findings, together with thermodynamic quantities for the enzyme, suggest that the thermal conformation changes in the enzyme protein occur around 40--43 degrees C and 61--64 degrees C. The Arrhenius plot of the rate constant of heat inactivation at pH 6.8 was bent at 73 degrees C. Thermodynamic data indicate that the enzyme is transformed from a heat stable form into a heat unstable form at 73 degrees C with temperature elevation. The critical points localized near the minimum, optimum, and maximum temperatures (40, 60, and 72 degrees C) of the cell growth, respectively.