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Appl. Environ. Microbiol., May 1997, 1847-1851, Vol 63, No. 5
H Kajikawa, M Amari and S Masaki
The glucose transport of mixed ruminal bacteria harvested from a holstein
cow fed 5.0 kg of Italian ryegrass and 1.5 kg of flaked corn a day was
investigated. The Eadie-Hofstee plot characterized two transport systems: a
high-affinity, low-velocity system and a low- affinity, high-velocity
system. The former system (K(m) = 16 microM; Vmax = 2.2 nmol/min/mg of
protein) is considered dominant under this feeding condition based on the
glucose concentration in the rumen (< 1 mM). In light of the facts that
the protonophore SF6847 and the lipophilic triphenylmethyl phosphonium ion
had no effect on the high- affinity system and an artificially generated
proton gradient and electrical potential across the cell membrane did not
increase glucose transport, a proton motive force is not be involved in the
system. On the other hand, from the facts that chlorhexidine inhibited
about 90% of the high-affinity system while iodoacetate showed no
significant effect, and a high phosphoenolpyruvate-dependent
phosphorylation of glucose was actually shown, the
phosphoenolpyruvate-dependent phosphotransferase system is considered the
main system in the high- affinity system. Moreover, as shown by the facts
that harmaline inhibited about 30% of the high-affinity system and the
artificially generated sodium gradient across the cell membrane
significantly stimulated glucose transport, this system also includes
sodium symport to some degree. The high-affinity system was sensitive to a
decrease in pH (< 6.5) and was inhibited by the presence of sucrose,
mannose, and fructose.
Copyright © 1997, American Society for Microbiology
Glucose transport by mixed ruminal bacteria from a cow
Department of Animal Nutrition, National Institute of Animal Industry, Ibaraki, Japan. kajikawa@niai.affrc.go.jp
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