3-Glucuronidase mammalian, activity

Table I gives approximate figures for the /3-glucuronidase activity of nearly all known sources of the enzyme. It can be seen that the enzyme is universally distributed in mammalian tissues and body fluids. This generalization probably extends to other vertebrates, and to insects and molluscs. The occurrence of the enzyme in micro-organisms is random, and bears no relation to their pathogenicity for man. The microbial enzyme may be adaptive or constitutive, and extracellular or intracellular the enzyme in Escherichia coli is adaptive and extracellular, whilst that in...

Glucuronidase Activity of Mammalian and Non-mammalian Tissues a. Phenolphthalein Liberated from Phenolphthalein p-o-Glucosiduronic Acid... 

The known sources which most closely approach the female-rat preputial gland in activity are the digestive juices of molluscs and of locusts. As shown for the rumen of the sheep,100 the contents of the mammalian large intestine probably owe most of their /8-glucuronidase activity to microbes, whilst in the small intestine the enzyme is probably mammalian in origin.40... 

Some preparations of mammalian /3-glucuronidase of high specific activity display a fall in net activity on dilution, an effect that can be prevented by adding a variety of substances (see Section IX, 2), of which albumin is, perhaps, the most satisfactory.49 138 When this phenomenon is encountered, the enzyme is assayed in the presence of an activator (see Fig. 4), and some of the figures quoted above were obtained in this way, as well as the kinetic constants quoted in subsequent Sections. (Failure to observe the dilution phenomenon with one highly-active preparation,80 although the customary activation was seen with substances like albumin, may be explained by the fact that the enzyme had undergone partial inactivation.)... 

The only non-mammalian /8-glucuronidase that has been subjected to systematic purification is the enzyme from sheep-rumen microorganisms. After repeated ammonium sulfate fractionation, Marsh101 obtained a colorless preparation with a specific activity of 1,900 (400-fold purification and 2% recovery). The final product gave a linear, specific-property, solubility test from which a figure of 2,200 was derived for the ultimate specific activity of the enzyme, but it was considered that the enzyme may have formed a solid solution with inactive protein. 

Mammalian /3-glucuronidase shows a shift in optimum toward a more alkaline pH in the presence of certain anions, such as deoxyribonucleate (see Fig. 4) and phthalate,8 49 8activity curve may previously have displayed (see Section IX, 2). Certain heavy-metal ions in trace amounts cause a shift in the optimum toward a more acid pH... 

Ox-liver /3-glucuronidase was found to be stable to 30 minutes of heating at 50°, but there was considerable inactivation42 at 55°. Heating a limpet preparation (of pH 5) for 5 minutes caused a 15% inactivation86 of /3-glu-curonidase at 60° and 35% at 70°. Within the range of temperature-stability of the enzyme, mammalian /3-glucuronidase activity was approximately doubled for every 10° rise in temperature.81 -147 1 66 This would also appear to be true of mollusc preparations.107171 ... 

Values for Km, the dissociation constant of the active, enzyme-substrate complex, for mammalian /3-glucuronidase and various substrates are shown in Table V. Table VI gives the values of Km that have been recorded for non-mammalian /3-glucuronidase preparations. Most of the figures have... 

Glucuronidase from mammalian and non-mammalian sources, including the purified enzyme from female-rat preputial gland, often displays marked inhibition in the presence of excess substrate. The number of substrate molecules per active-enzyme center in the inactive enzyme-substrate complex ig24.100. ice.167 usuaUy 2, but values of166 3 and143 4 have also been reported. 

Dissociation Constants (Km) of the Active Enzyme-substrate Complex for Mammalian -Glucuronidase and Various Substrates... 

It seems feasible that traces of heavy-metal ions may have some bearing upon certain features of the action of mammalian /3-glucuronidase, such as the fall in net activity seen on dilution of highly purified preparations (see Section IV), the inhibitory action of the unknown constituents of urine,185 190 and the pH optimum at pH 3.4 observed by Mills, Paul, and Smith166 but by no other workers (see Section VI). The presence of traces of Cu in the assay mixture would provide a completely satisfactory explanation of the variable effects reported with L-ascorbic acid (see Section IX, 2).196s... 

A mammalian system has been used to determine the fate in vivo of bovine jS-D-glucuronidase administered intravenously to mice that are deficient in the enzyme sensitive and reliable discrimination between bovine-liver and residual, murine-tissue jS-D-glucuronidase activities was achieved by inactivation of the former with heat. The bovine activity was cleared rapidly from circulation following injection, and was recovered almost exclusively in the liver, where 72% is localized in the lysosomes. The mammalian system provides an in vivo model that enables the protection and delivery of an exogenous enzyme to be evaluated prior to replacement trials in patients with inherited diseases caused by an enzyme deficiency. 

The inhibition of giucaric acids demonstrated that gluearo (1—>4) lactone was the active constituent present as a contaminant in aqueous solutions of glucarate (Lewy, 1952). Glucarate as endogenous inhibitor of glucuronidase in mammalian tissues will be described later. 

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