Baicalinase, a plant β-glucuronidase

Abstract

Baicalinase, a hydrolytic enzyme from the root of Scutellaria baicalensis hydrolysed phenolphthalein [beta]-D-glucuronide. The pH optimum was 4.4-5.5 with a sharp peak being obtained with more concentrated buffer (0.25N). The KM value was 5.6 x 10-4M. Competitive inhibition was found with Saccharo-1-4-lactone, (-) Menthyl [beta]-glucuronide, veratroyl glucuronide, [alpha] -ethylhexanoyl glucuronide, chrysin glucuronide and scutellarin, but there was no inhibition with saccharo-3:6-lactone, and [alpha]-glucuronides or [beta]-galacto and glucofuranuronides. KM values for saccharo -l:4-lactone and methyl [beta]-glucuronide were 2.0 x 10-4 and 1.39 x l0-2M. Several other species were tested but only S. albida contained an enzyme resembling baicalinase. Mouse-liver [beta]-glucuronidase hydrolysed chrysin glucuronide and baicalin and the KM values were 8 and 10 x 10-6M. It was inhibited by saccharate. It is concluded that baicalin and chrysin glucuronide are [beta]-D-glucopyranuronides.