A strong correlation between the increase in number of proline residues and the rise in thermostability of five Bacillus oligo-1,6-glucosidases

Abstract

A p-nitrophenyl-α-d-glucopyranoside-hydrolysing oligo-1,6-glucosidase (dextrin 6-α-d-glucanohydrolase, EC 3.2.1.10) of Bacillus sp. KP 1071 capable of growing at 30°–66°C was purified to homogeneity. The molecular weight was estimated to be 62,000. The amino-terminal amino acid was methionine. The enzyme shared its antigenic groups in part with its homologous counterpart from Bacillus thermoglucosidasius KP 1006 (obligate thermophile), but did not at all with any one of oligo-1,6-glucosidases from Bacillus cereus ATCC 7064 (mesophile), Bacillus coagulans ATCC 7050 (facultative thermophile) and Bacillus flavocaldarius KP 1288 (extreme thermophile). A comparison of amino acid composition showed that the proline content increased greatly in a linearity with the rise in thermostability in the order, mesophile → facultative thermophile → KP 1071 → obligate thermophile → extreme thermophile enzymes.