Mw. Fields et Jb. Russell, The glucomannokinase of Prevotella bryantii B(1)4 and its potential role in regulating beta-glucanase expression, MICROBIO-UK, 147, 2001, pp. 1035-1043
Prevotella bryantii B(1)4 has a transport system for glucose and mannose, b
ut beta -glucanase expression is only catabolite-repressed by glucose. P. b
ryantii B(1)4 cell extracts had ATP-dependent gluco- and mannokinase activi
ties, and significant phosphoenolpyruvate- or GTP-dependent hexose phosphor
ylation was not observed. Mannose inhibited glucose phosphorylation (and vi
ce versa), and activity gels indicated that a single protein was responsibl
e for both activities. Glucose was phosphorylated at a faster rate than was
mannose [V-max 280 nmol hexose (mg protein)(-1) min(-1) versus 60 nmol hex
ose (mg protein)(-1) min(-1), respectively] and glucose was a better substr
ate for the kinase (K-m 0.12 mM versus 1.2 mM, respectively). The purified
glucomannokinase (1250-fold) had a molecular mass of 68 kDa, but SDS-PAGE g
els indicated that it was a dimer (monomer 34.5 kDa). The N-terminus (25 re
sidues) had an 8 amino acid segment that was homologous to other bacterial
glucokinases. The glucomannokinase was competitively inhibited by the nonme
tabolizable glucose analogue 2-deoxyglucose (2DG), and cells grown with glu
cose and 2DG had lower rates of glucose consumption than did cells given on
ly glucose. When the ratio of 2DG to glucose was increased, the glucose con
sumption rate decreased and the beta -glucanase activity increased. The glu
cose consumption rate and the glucomannokinase activity of cells treated wi
th 2DG were highly correlated (r(2) = 0.98). This result suggested that glu
comannokinase activity was either directly or indirectly regulating beta -g
lucanase expression.