Evidence for beta-galactosidase catalyzed hydrolysis of paranitrophenyl-beta-D-galactopyranoside anchored in cyclodextrins.
The absorption maximum of p-nitrophenol upon mixing with molar equivalents of alpha-cyclodextrin (alpha-CD) or hydroxypropyl-beta-cyclodextrin (HPB) showed nearly 5 nm shift to the longer wavelength region, indicative of complex formation, while beta-cyclodextrin (beta-CD), gamma-cyclodextrin (gamma-CD) and hydroxyethyl-beta-cyclodextrin (HEB) produced only a marginal shift of about 1-2 nm, suggestive of a weaker interaction. It has been shown by circular dichroism spectral studies that the aglycon part of p-nitrophenyl-beta-D-glycoside (PNPG) is also encapsulated by alpha-cyclodextrin. The encapsulated form of PNPG could be hydrolyzed by beta-galactosidase, the temperature and pH-optima for hydrolysis of anchored substrates being essentially identical to that of free substrate. However, small but consistent increase in Km values were obtained for alpha-cyclodextrin-, HEB- and HPB-anchored substrates. The kcat values also registered an increase for the HEB- and HPB-anchored substrates. However, there was no increase in kinetic efficiency (kcat/Km) of enzyme. The inhibition noted at higher concentrations of HEB- and gamma-cyclodextrin-anchored PNPG but not with o-nitrophenyl-beta-D-galactoside (ONPG)-cyclodextrin mixture suggests that PNPG-cyclodextrin complexes were responsible for the inhibition. Taken together, these results suggest that the enzyme catalyses the hydrolysis of anchored substrates.
Jyothirmayi
N
N
Department of Food Chemistry, Central Food Technological Research Institute, Mysore, India.
Ramadoss
C S
CS
D003505:Cyclodextrins / Q000494:pharmacology*; D004926:Escherichia coli / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D009598:Nitrophenylgalactosides / Q000378:metabolism*; D013816:Thermodynamics; D001616:beta-Galactosidase / Q000378:metabolism*
D003505:Cyclodextrins; D009598:Nitrophenylgalactosides; C059200:4-nitrophenylgalactoside; D001616:beta-Galactosidase