3-Glucuronidase sources

The first proteins from transgenic plants to reach commercial status were avidin and P-glucuronidase (GUS) both of which are used as diagnostic agents in molecular biology. An important principle demonstrated by these case studies is that molecular farming in cereals can be an economical alternative even when the natural source of a protein is abundant (i.e. egg whites for avidin, and Escherichia coli for GUS) and where a market is already established. 

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...

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... 

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. 

Values of Ki for Competitive Inhibitors Acting on 0-Glucuronidase from Non-mammalian Sources ... 

Strictly speaking, an enzyme can only provisionally be classified as a /8-glucuronidase before its action has been shown to be purely hydrolytic— by the isolation of D-glucuronic acid as well as the aglycon. This consideration is of particular importance when whole, bacterial suspensions are employed as a source of the enzyme. 

One proposed mechanism of MBOCA excretion suggests that very little MBOCA is excreted into the bladder as the free amine since most of the MBOCA in the renal perfusate may be present in the form of the p-N-glucuronide conjugate (Cocker et al. 1990). Urine contains p-glucuronidase, and therefore, p-N-glucuronide may undergo some hydrolysis in the bladder. This is proposed as the source of free MBOCA in the urine. 

The Golgi apparatus is also believed to concentrate lysosomal enzymes and to be at the source of small vacuoles filled with acid hydrolases, which constitute the primary lysosomes. The evidence invoked in support of this hypothesis is based primarily on histochemical and electron microscopic observations that have demonstrated the presence of such lysosomal enzymes as acid phosphatase, j8-glucuronidase, sulfa-tase, and esterases in the Golgi apparatus. 

The rate of removal of purified P-D-glucuronidases from rats following intravenous infusion depended on the source of the enzyme. Thus, the P-D-glucuronidase from rat serum was cleared more slowly from circulation than that from rat preputial glands. The lysosomal compartment of rat liver has an important role in the removal of circulating tris and glycoside hydrolases. ... 

Injection of alkyl phosphates into rats raised the level of P-D-glucuronidase activity in their sera without affecting the levels of lysosomal hydrolases and cholinesterase. Dibutyl and tributyl phosphates were most and equally effective, the levels of P-D-glucuronidase activity increasing 120- and 90-fold after 1 and 2 h, respectively. The increase in enzymic activity elicited with tributyl phosphate correlated with a lowering of the enzymic activity in the liver microsomes, which appear to be the main source of the excess of P-D-glucuronidase activity in the serum. 

Enzyme P-glucuronidase suspension from E. coli K 12 source (EC 3.2.1.31). At 37°C the solution should have at least 140 U/mL of activity. 

Pregnancy urine has been found to be a rich source of estrogens and related compounds. They are generally excreted as sulfates or glucu-ronosides, and are liberated from the esters by acid hydrolysis, phenol-sulfatase, and j8-glucuronidase. The 18-carbon steroids isolated from mammalian urine show close similarity (Table VIII and Fig. 18). They... 

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