Preparation and properties of beta-glucuronidase

A thermostable β-glucuronidase obtained by directed evolution as a reporter gene in transgenic plants

A β-glucuronidase variant, GUS-TR3337, that was obtained by directed evolution exhibited higher thermostability than the wild-type enzyme, GUS-WT. In this study, the utility of GUS-TR337 as an improved reporter was evaluated. The corresponding gus-tr3337 and gus-wt genes were independently cloned in a plant expression vector and introduced into Arabidopsis thaliana. With 4-MUG as a substrate, plants containing the gus-wt gene showed no detectable β-glucuronidase activity after exposure to 60°C for 10 min, while those hosting the gus-tr3337 gene retained 70% or 50% activity after exposure to 80°C for 10 min or 30 min, respectively. Similarly, in vivo β-glucuronidase activity could be demonstrated by using X-GLUC as a substrate in transgenic Arabidopsis plants hosting the gus-tr3337 gene that were exposed to 80°C for up to 30 min. Thus, the thermostability of GUS-TR3337 can be exploited to distinguish between endogenous and transgenic β-glucuronidase activity, which is a welcome improvement in its use as a reporter.

Factor affecting the endogenous β-glucuronidase activity in rapeseed haploid cells: how to avoid interference with the Gus transgene in transformation studies

The gus gene is one of the most frequently used reporter genes in transgenic plants. However, this gene can only be used if the selected plant species does not show endogenous GUS activity. Rapeseed (Brassica napus) microspores and microspore-derived embryos (MDEs) were found to exhibit high activity of endogenous β-glucuronidase which interferes with the expression of bacterial β-glucuronidase that was transferred into these tissues by biolistic transformation. In order to eliminate this background activity from rapeseed MDEs, different pHs of the assay buffer (5.8, 7 and 8) with or without methanol in the reaction buffer and incubation of these tissues at different temperatures (24°C, 38°C and 55°C) were investigated. To avoid this problem in microspores, two incubation temperatures (38°C and 55°C) at different periods after GUS assay (4, 24 and 48h) and in the presence of 1mM potassium ferricyanide and 1mM potassium ferrocyanide were tested. The endogenous GUS activity was significantly decreased in transformed and untransformed MDEs, when the phosphate buffer was adjusted to pH 8 and 28% methanol in the reaction solution was used. In rapeseed microspores, use of 1mM potassium ferricyanide and 1mM potassium ferrocyanide in the reaction buffer enhanced the expression rate of gus transgene rather than endogenous GUS activity where the high levels of gus transgene expression was observed 4h after histochemical GUS assay. Incubation of rapeseed microspores and MDEs at 55°C completely eliminated the endogenous GUS activity. In this study, we also examined changes in endogenous GUS activity in rapeseed MDEs at several stages including the globular, heart, torpedo and cotyledonary stages. The level of endogenous GUS activity was increased 4.33 folds in heart embryos, 6.54 folds in torpedo embryos and 8.5 folds in cotyledonary embryos. Furthermore, the level of GUS activity increased 1.72 folds in MDEs of B. napus in 12-h treatment with 2μM gibberellic acid.

An ELISA-like assay for hyaluronidase and hyaluronidase inhibitors

Hyaluronic acid (HA) is a prominent molecule in the extracellular matrix and is enriched whenever there is rapid tissue proliferation, regeneration and repair. HA is degraded in part by hyaluronidases (HA'ases) that are not well characterized. We have developed a novel ELISA-like rapid assay for HA'ases and their inhibitors. The assay is based on a high affinity biotinylated HA-binding peptide derived from tryptic digests of proteoglycan core protein of bovine nasal cartilage and the avidin-biotin reaction. HA-coated plates were incubated with serial dilutions of Streptomyces HA'ase, and the undegraded HA was measured. This established a standard curve for HA'ase activity against which all unknown enzyme samples were compared. The assay is easily modified to also serve a measure of HA'ase inhibitors. For detection of inhibitors, aliquots of sample were preincubated with a known activity of HA'ase and inhibition of HA degradation by the mixture was measured. We have used this assay to document the presence of potent HA'ase inhibitors in fetal calf sera. These techniques will aid in the purification and characterization of Ha'ases and their inhibitors.

Hyaluronidase activity in embryonic chick heart muscle and cushion tissue and cells

Hyaluronidase activity was compared in embryonic chick cardiac cushion and noncushion segments, as well as in cultures of mesenchyme derived from cardiac cushion endocardium (cushion tissue-enriched cultures) and in cultures of myocardial cells at stages critical to heart valve and septum development. Enzyme levels were higher in both heart tissue regions at periods of active cushion tissue mesenchyme migration than after migration ceases, and higher in the cushion region than in the noncushion region at both periods. Hyaluronidase was measured in cells and medium in both types of cultures, with five times greater activity found in the myocardial cultures. The cardiac hyaluronidase from cells and medium of both culture types had an estimated molecular weight of 41,000 to 44,000 and degraded hyaluronate and, to a lesser degree, chondroitin sulfate, at an acidic pH optimum. Ion-exchange chromatography demonstrated that in both culture types, a proportion of the secreted enzyme was more acidic than that found in the cell layer. These studies indicate the potential for hyaluronate degradation by the major cell types present in the developing heart at early stages and that the enzyme responsible is probably a lysosomal enzyme. Therefore, hyaluronate internalization is a likely requirement for degradation, and thus, the turnover of hyaluronate in developing heart valves is more complex than the extracellular degradative process suggested by histochemical data.

Identification, purification, and partial characterization of an organic anion binding protein from rat liver cell plasma membrane

Uptake of bilirubin, sulfobromophthalein (BSP), and other organic anions by the liver is a process with kinetics consistent with carrier mediation. The molecular basis of this transport mechanism is unknown. In the search for the putative organic anion carrier or receptor, the interaction of BSP with rat liver cell plasma membrane (LPM) has been studied. Specific binding of [(35)S]BSP to LPM was determined using a filtration assay. Results revealed high affinity (K(a) = 0.27 muM(-1)), saturable (6.3 nmol/mg protein) binding, which was eliminated after preincubation with trypsin. Although [(35)S]BSP was strongly bound to LPM, the binding was rapidly reversible, preventing direct identification and study of a specific binding site(s). To avoid this problem, a photoaffinity probe was devised, in which [(35)S]BSP is covalently bound to LPM after exposure to ultraviolet light. Subsequent sodium dodecyl sulfate gel electrophoresis and fluorography revealed radioactivity predominantly associated with a single 55,000-mol wt protein. A protein with identical electrophoretic mobility was purified from deoxycholate solubilized LPM after affinity chromatography on glutathione-BSP-agarose gel. This protein migrated as a single band on sodium dodecyl sulfate gel electrophoresis and on urea gel isoelectric focusing. It contained 1-2 residues of sialic acid per 55,000-dalton protein, and was immunologically distinct from rat albumin and ligandin. It bound bilirubin with a K(d) of 20 muM, as determined by tryptophan fluorescence quenching. Although the high affinity of this LPM protein for organic anions suggests that it may function as a hepatocellular organic anion receptor, its role in transport of these compounds is unknown.

A selected ion monitoring method for glutethimide and six metabolites: application to blood and urine from humans intoxicated with glutethimide

A method employing selected ion monitoring for the analysis of glutethimide and six of its metabolites has been developed. Hydroxylated metabolites analyzed as trifluoroacetates, included 4-hydroxyglutethimide, (1-hydroxyethyl)glutethimide and p-hydroxyglutethimide. The unchanged drug, 3-dehydroglutethimide, desethylglutethimide and the internal standard, [2H5]glutethimide, were chromatographed underivatized on OV-225. The assay was used to measure drug and metabolites in the plasma and urine of patients intoxicated with glutethimide. High levels (e.g. 20--35 microgram ml-1) of unconjugated 4-hydroxyglutethimide, an active metabolite, were found in all patients at a time when levels of unchanged drug were lower and declining. Other unconjugated and conjugated metabolites were found in relatively low concentrations in the plasma (i.e. less than 4 microgram ml-1). The major urinary metabolites were conjugates of 4-hydroxyglutethimide and (1-hydroxyethyl)glutethimide. The unchanged drug and other conjugated and unconjugated metabolites were found in lower amounts in the urine. Normal plasma half-lives of glutethimide and the relatively small amounts in urine of unchanged drug and unconjugated metabolites indicated that drug elimination was not markedly impaired in the intoxicated patients.

Isolation, determination of structure and synthesis of the acid-labile conjugate of aldosterone

1. After administration of 600mg of 3H-labelled aldosterone to human volunteers, 57 mg of homogeneous acid-labile conjugate was isolated from the urine and identified as aldosterone 18 beta-D-glucosiduronic acid. 2. Esterification and acetylation of the conjugate gave a tetra-acetate methyl ester, which, by measurement of the optical rotation and nuclear-magnetic-resonance spectrum, was shown to be a beta-glucosiduronate. This tetra-acetate methyl ester was synthesized in approx. 10% yield by the Koenigs-Knorr procedure. 3. Removal of the acetyl and methyl ester groups from the tetra-acetate methyl ester with alkali was accompanied by almost complete isomerization at C-17 to give 17-isoaldosterone 18 beta-D-glucosiduronic acid. 4. To prevent inversion at C-17 during removal of the acetate and ester groups of beta-glucosiduronate (a) the 3,20-disemicarbazone was prepared, (b) the acetate and ester groups were removed from the disemicarbazone by treatment with alkali, and (c) the semicarbazone groups were removed from the product at pH 2.0, and aldosterone 18 beta-D-glucosiduronic acid was obtained in 47% overall yield. 5. In the presence of components used to synthesize beta-glucosiduronate by the Koenigs-Knorr reaction this substance is converted slowly into the alpha-glucosiduronate; this conversion is responsible, in part, for the low yield of beta-glucosiduronate. 6. Two additional conjugates were obtained in the Koenigs-Knorr reaction; a provisional structure was assigned to one substrate. The other substance is a C-18 alpha-glucosiduronate. Removal of the acetyl and ester groups from C-18 alpha-glucosiduronate gave the alpha-glucosiduronic acid in 84% yield and the 17-isoaldosterone alpha-glucosiduronic acid in 12% yield. 7. The rate at which several types of beta-glucuronidase hydrolyse the foregoing steroidal alpha- and beta-glucosiduronic acids is given.

Purification and characterization of lysosomal -glucuronidase from human placenta

1. Subcellular fractions of human placenta were prepared by nitrogen-bomb homogenization and differential centrifugation. 2. beta-Glucuronidase from placental lysosomes was purified 2100-fold on a protein basis. 3. The lysosomal enzyme, at different stages of purification, was characterized by using 4-methylumbelliferyl beta-d-glucuronide and phenolphthalein beta-d-glucuronide as substrates. 4. Only one isoenzyme of beta-glucuronidase was found in placenta; the enzyme in the endoplasmic reticulum appeared to be the same as the lysosomal enzyme. 5. The isoenzyme contained in normal plasma was different from that of the placenta. 6. The elevated beta-glucuronidase activity found in plasma obtained during pregnancy was due to increased activity of the normal plasma isoenzyme; no contribution was made by placental isoenzyme. 7. Plasma contained a heat-stable, non-diffusible activator of placental beta-glucuronidase. 8. A heat-stable competitive inhibitor of placental and plasma beta-glucuronidase was also present in plasma.

Extracellular transglucosylase and alpha-amylase of Streptococcus equinus

Culture filtrates of Streptococcus equinus 1091 contained alpha-amylase and transglucosylase. The effects of calcium carbonate, age of inoculum, concentration of maltose, and duration of the fermentation on alpha-amylase and transglucosylase production were determined. The extracellular alpha-amylase was purified 48-fold and was free of transglucosylase activity. The alpha-amylase (amylose substrate) required Cl(-) for maximum activity; ethylenediaminetetraacetic acid (EDTA) partially inhibited activity, but CaCl(2) prevented EDTA inhibition. The temperature optimum was 38 C at pH 7.0, and the pH optimum was 7.0 at 37 C in the presence of CaCl(2). Predominant final products of amylose hydrolysis, in order of decreasing prevalence, were maltose, maltotriose, maltotetraose, and glucose. The alpha-amylase showed no evidence of multiple attack. The extracellular transglucosylase was purified 27-fold, but a small amount of alpha-amylase remained. Transglucosylase activity (amylose substrate) was not increased in the presence of CaCl(2). The temperature optimum was 37 C at pH 6.5, and the pH optimum was 6.0 at 37 C. Carbohydrates that served as acceptors for the transglucosylase to degrade amylose were, in order of decreasing acceptor efficiency: d-glucose, d-mannose, l-sorbose, maltose, sucrose, and trehalose. The extracellular transglucosylase of S. equinus 1091 synthesized higher maltodextrins in the medium when the cells were grown in the presence of maltose.

Metabolism of D-glucuronolactone in mammalian systems. Inhibitory properties of the products of D-glucuronolactone-dehydrogenase action

1. d-Glucuronolactone was converted into d-glucaro-(1-->4)-lactone, a beta-glucuronidase inhibitor, probably via the intermediate d-glucaro-(1-->4)-(6-->3)-dilactone, by a dehydrogenase in human-liver extracts. 2. Similar experiments with mouse-liver extracts appeared to yield only d-glucaric acid or a non-inhibitory lactone. 3. A strong beta-glucuronidase inhibitor was present in mouse liver after the intraperitoneal administration of d-glucuronolactone. 4. d-Glucarodilactone decomposed spontaneously in aqueous solution to give 25% of d-glucaro-(1-->4)-lactone; the percentage conversion was unaffected by human-liver homogenates. but considerably increased by mouse-liver or pig-liver fractions.