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Group transfer reactions catalyzed by enzymes have assumed a position of intense interest in contemporary enzymology (1).Well known examples of radicals capable of being transferred in such reactions are methyl, glycosyl, aeetyl, phosphoryl, pept,idyl, nucleosidyl, and nucleotidyl, in addition to the transport of hydrogen as seen with the familiar nuoleot.idecoenzymes.In this paper we wish to report experimental evidence which establishes t,he phenomenon of an efficient enzyme-catalyzed transfer of the glucuronyl radical from a variety of donor substrates to a number of acceptor alcohols.This is accomplished by a soluble, stable, highly purified cell-free enzyme from liver which is in many respects indistinguishable from @-glucuronidase.These data supplement and extend the observations first reported in 1956 (2). MethodsAnalytical Approach-The donor substrate, usually phenolphthalein glucosiduronic acid plus a suitable acceptor molecule, was incubated with the purified enzyme for 15 minutes in most of the experiments.The reaction was stopped and the aqueous phase was analyzed for the liberated donor aglycone (3).Unhydrolyzed donor substrate was removed by extraction with ethyl acetate and glucuronic acid and glucosiduronic acid were determined (4).With the simple alcohols used in this study, conjugated products were formed which were not extracted by ethyl acetate at acid pH, and t,herefore these products constituted the newly formed glucosiduronic acid component.The difference in micromoles between released glucuronyl (total unextracted glucuronic acid) and free glucuronic acid or between liberated aglycone and free glucuronic acid represents the extent of
Fishman et al. (1957) studied this question.