title: The effect of methanol and dioxan on the rates of the beta-galactosidase-catalysed hydrolyses of some beta-D-galactrophyranosides: rate-limiting degalactosylation. The ph-dependence of galactosylation and degalactosylation.
abstract: 1. The effect of methanol on the beta-galactosidase-catalysed hydrolysis of some nitrophenyl beta-d-galactopyranosides has been studied under steady-state conditions. 2. The initial fractional rate of increase of k(cat.) as a function of methanol concentration with 2,4- and 3,5-dinitrophenyl beta-d-galactopyranosides, but not with the other substrates studied, indicated that degalactosylation of the enzyme was rate-limiting. 3. The decrease in k(cat.) at high methanol concentrations for these substrates is considered to arise from causes other than galactosylation becoming rate-limiting. 4. Both galactosylation and degalactosylation of the enzyme require protonation of a group of pK(a) approx. 9.
mesh_terms: D001665:Binding Sites; D002021:Buffers; D055598:Chemical Phenomena; D002621:Chemistry; D004140:Dinitrophenols; D004147:Dioxins; D005696:Galactosidases; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008433:Mathematics; D000432:Methanol; D009596:Nitrophenols; D011485:Protein Binding
chemical_list: D002021:Buffers; D004140:Dinitrophenols; D004147:Dioxins; D009596:Nitrophenols; D005696:Galactosidases; D000432:Methanol