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The inhibition of P-glucuronidase by mam ng animals maintained on normal diets in metabolism cages. steroids, from the fl-D-glucosiduronic acid con-The rat and guinea-pig exereta were separated by filtration, jugates. P-Glucuronidase assay is normally con-and the faeces washed with water, before the combined ducted with a chromogenic substrate, the enzymic urine and washings were tested. Urines were stored at 0' if hydrolysis of which may be diminished in the examined within 24 hr. of collection, or otherwise at -20°. glucuronidase, however, mammnalian urine con-for 40 min. after adjustment with 3N-HCl to pH 2-0-2-2, tains trueenzymeinhibitrs Abul-Fadl(1957) followed by readjustment with NaOH to pH 4-0-45, or tamns true enzyme inhibitors. Abul-Fadl (1957) (b) at 100°for 15 min. after adjustment with 0-1 N-NaOH to found both dialysable and non-dialysable material pH 7-5-8-0, follQwed by readjustment with HCI to pH 60-in human urine which was inhibitory to /-gluc-6-5. The inhibitory power was maximal after treatment

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The method is capable of extension to the preparation of other nucleoside polyphosphates labelled with radioactive phosphorus. SUMMARY 1. The reaction of orthophosphate with adenosine 5'-monophosphate, diphosphate and triphosphate in the presence of NN'-dicyclohexylcarbodiimide has been used for the preparation of labelled adenosine polyphosphates.2. The adenosine diphosphate so prepared is labelled exclusively in the terminal phosphate group. The adenosine triphosphate and adenosine tetraphosphate so prepared are labelled in the terminal phosphate group, and to a lesser extent in the penultimate phosphate group.3. A feature of the method is that carrier-free labelled orthophosphate can be used without prior dilution with unlabelled orthophosphate.4. The reaction ofpyrophosphate with adenosine 5'-monophosphate in the presence of NN'-dicyclohexylcarbodiimide has been used for the preparation of labelled adenosine triphosphate. 5. The adenosine triphosphate so prepared is labelled in the f,and y-phosphate groups to an equal extent.6. An improved method for the preparation of NN'-dicyclohexylcarbodiimide is described.I am indebted to Professor H. A. Krebs for the privilege and pleasure of working in his laboratory. I wish to thank Mr R. Hems for discussions and much helpful advice, Mr K. Jones for advice on the use of ultraviolet photography, Dr H. L. Kornberg for advice on autoradiography, Dr W. Bartley for a gift of potato apyrase and Professor J.Baddiley for pointing out to me the necessity of the refluxing procedure in the preparation of N,N'-dicyclohexylthiourea.My thanks go to the Sigma Chemical Co., St Louis, Missouri, for a most generous gift of adenosine tetraphosphate.