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Query: EC:6.3.4.6 (urease)
 7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The existence of hysteresis phenomena in artificial enzyme membranes due to the coupling of simple kinetic enzyme properties with diffusion transport processes is reported. The intramembrane pH of a urease coating on the surface of a glass pH electrode exhibits a hysteresis loop when the pH of the bulk solution varies cyclically. The steady-state potential of a urease membrane, as a function of the substrate concentration in the bulk solution, also exhibits a memory effect. The influence of the membrane's history on its overall behavior is visualized by electron microscopy. We interpret the results in terms of a coupling between the enzyme reactions and diffusion processes, without taking into account molecular effects.
Proc Natl Acad Sci U S A 1977 Dec
PMID:Experimental evidence for a kinetic and electrochemical memory in enzyme membranes. 2 33

The behavior of an enzyme/membrane system containing urease is studied when an external electric field is applied. The device using a potential difference across the enzyme/membrane system is first described. Optimal operating conditions with respect to substrate concentration, ionic strength and pH are studied. Possible mechanisms of the change in membrane activity by electric field are discussed.
Biochim Biophys Acta 1979 Dec 07
PMID:Electric field effects on immobilized urease activity. 4 83

Experiments and appropriate mathematical models are presented in an attempt to elucidate and separate the effects of mass transfer and immobilization on the apparent kinetics of hydrolysis of urea by urease immobilized within a crosslinked gelatin film. Diffusion of urea through the gelatin matrix appears to exert the major influence on the observed kinetics. Diffusion coefficients are measured, and a model for the "effectiveness factor" is presented, accounting for this aspect of mass transfer control. A secondary, but significant, influence on apparent kinetics arises because the reaction products lead to an increased pH level which, because of diffusion resistance, remains high within the gelatin matrix. For pH levels in the 6.7 to 9.0 range the activity of urease is a strongly decreasing function of pH. An approximate model accounting for ionic equilibrium allows this pH-diffusion effect to be introduced in such a way as to lead to predictions of the apparent kinetics that are compared with experimental observations. Examination of these results indicates that the immobilization procedure leads to some loss of activity due to an interaction of the gelatin crosslinking reaction with the enzyme itself.
Biotechnol Bioeng 1979 Dec
PMID:Hydrolysis of urea by gelatin-immobilized urease: separation of kinetic and diffusion phenomena in a model immobilized-enzyme reactor system. 4 51

The localization of some enzymic activities in cell fractions of Ureaplasma urealyticum was studied. A quantitative evaluation of the effectiveness of several cell lysis procedures was obtained by using labeled membranes and sucrose density gradient centrifugation. Ultrasonic treatment was found to be the most effective procedure for lysing the cells, whereas digitonin and osmotic shock caused the lysis of only 70 and 50% of the cells, respectively. The localization of selected enzymes in Ureaplasma cells resembled that found in other Mycoplasma species. Adenosine triphosphatase, ribonuclease, deoxyribonuclease, and p-nitrophenylphosphatase activities were located exclusively in the membrane fraction, whereas urease and L-histidine ammonia-lyase were located in the cytoplasm.
J Bacteriol 1978 Dec
PMID:Cell fractions and enzymatic activities of Ureaplasma urealyticum. 21 22

The Oxi/Ferm test system was evaluated for accuracy and reliability for identification of nonfermentative and oxidase-positive fermentative bacteria by using 375 bacterial strains obtained from stock culture and clinical specimens. The Oxi/Ferm system is a compartmentalized tube containing eight media to provide nine biochemical test results. When combined with the oxidase test, the results corresponding to the positive reactions are totaled and the composite number is located in the coding manual to identify the organisms. The 375 isolates studied were evaluated for accuracy of identification, using both the original and revised code manuals. In comparison with the conventional media used, there was 100% correlation in tests for hydrogen sulfide and indole production, over 96% for nitrogen gas, arginine, and urease, over 92% for xylose and dextrose oxidation, and less than 90% for citrate utilization and dextrose fermentation. There was an overall accuracy in identification of 89.3% using the original manual, with accuracy revised slightly upward to 90.7% using the revised manual. There was 100% accuracy in identification with 44.0% of the strains tested (11 species) using the original manual and with 66.1% (16 species) using the revised manual. Thirteen of the 40 original misidentifications and 14 of 35 revised misidentifications resulted from failure to code and were unidentifiable by Oxi/Ferm. The remainder were incorrectly identified or could not be differentiated from closely related strains. Eleven strains of Alcaligenes odorans were correctly identified using the original code, whereas no code was provided in the revised manual. The Oxi/Ferm system is both simple and rapid and is satisfactory for identification of the more common isolates.
J Clin Microbiol 1977 Dec
PMID:Evaluation of the oxi/ferm tube system with selected Gram-negative bacteria. 33 24

In order to improve the isolation and identification of yeasts in a cancer research hospital, a protocol was developed utilizing an improved blood culture methodology and a four-test schema for rapid yeast identification. The blood culturing technique, based upon centrifugation, has shown a ten-fold increase in isolation of fungi from blood and has provided for: quantitation or organisms, unlimited selection of media and atmospheres for primary culturing, and a 1:200 dilution of microorganisms away from serum antimicrobial factors and antibiotics. The four-test schema, which may be adapted for the identification of any unknown yeast in pure culture, consists of a dye pour plate auxanogram (DPPA), Tween 80-Oxgall-Caffeic acid (TOC), a rapid nitrate-reductase test (swab test) and Urea 'R' Broth. Using this protocol, over 95% of the clinical isolates received were correctly identified within 24 hours and 100% by 48 hours. By using DPPA, a 14 sugar assimilation pattern for each isolate was determined within 12 to 16 hours; and in some cases, as little as 6 hours. Growth on TOC yielded one of the following results: (1) Candida albicans and Candida stellatoidea sequentially produced germ tubes and chlamydospores in 3 hours and 24 hours, respectively; (2) Cryptococcus neoformans produced a brown pigment specific for its identification in 12 hours or less. The swab test gave results on nitrate utilization in less than 15 minutes and urease was detected within 4 hours.
Mycopathologia 1978 Dec 18
PMID:Isolation and rapid identification of yeasts from compromised hosts. 37 Jun

Cell-free extracts prepared from Pseudomonas aeruginosa cells, cultured in a medium containing allantoin as sole nsource of carbon, nitrogen and energy and harvested in the stationary phase, contain an enzymicly inactive allantoinase-inhibitor complex. Pure inhibitor was isolated by dissociation of this complex followed by gelfiltration. The inhibitor had a molecular weight of about 5500 daltons. Association between inhibitor and allantoinase was demonstrated by gelfiltration and by polyacrylamide gel-electrophoresis. The inhibitor was unstable in the absence of 1 M urea and the inactivation was accompanied by aggregate formation and appearance of urease activity. The inhibitor was also isolated from cells containing urease but no allantoinase. It was concluded that the inhibitor is a subunit of urease. Inhibitors isolated from P. aeruginosa and P. acidovorans cells were active against both allantoinase from P. aeruginosa and allantoinase from P. acidovorans.
Arch Microbiol 1976 Dec 01
PMID:Inactivation of allantoinase from Pseudomonas aeruginosa by a subunit of urease. 82 28

The diagnosis of obligately aerobic Gram-negative rods in the clinical laboratory may encounter difficulties since media used for Enterobacteriacae are only partially usable for the diagnosis of this group of bacteria (Psuedomonas, Xanthomonas, Alcaligenes, Achromobacter, Brucella, Bordetella, Flavobacterium, Moraxella, Acinetobacter, and some still unnamed taxa). We have developed a diagnostic scheme, based on recent publications in the field and representing an extension of earlier tables from this and other laboratories, which attempts to classify a maximal number of obligately aerobic Gram-negative rods with a minimal number of tests. The scheme, employed on 4051 strains, used blood agar and MacConkey Agar as isolation media. Growth characteristics on these media and microscopic morphology may be of help, but only the type of growth on Triple Sugar Iron (or Kligler's) Agar is characteristic for the group as a whole (no growth in the butt, alkalinization or no pH change on the slant). A primary identification series employs tests for oxidase (Kovacs), oxidation of glucose and xylose (in OF medium), deoxyribonuclease and indole (in DNase Test Agar with Methyl Green), nitrate reduction (in Indole Nitrite Medium), motility (hanging drop), and fluorescein production (on Flo Agar). Results of Kirby-Bauer antimicrobial sensitivity testing serve as additional (colistin) or confirmatory criteria. Incubation is at 30 degrees C for 24-48 hrs. If a diagnosis is not possible than, a secondary series, including tests for lysine decarboxylase (tablets), 4 hr urease, esculin hydrolysis, growth at 42 C and on SS Agar, gelatin liquefaction, and flagellar staining may have to be used, and read after 4-24 hrs at 30 degrees C. Five tables, drawn up according to oxidase, glucose, and xylose reactions, serve to identify the species or taxa. Biotypes cannot be differentiated. The scheme will need updating as more knowledge of these bacteria will become available.
Zentralbl Bakteriol Orig A 1976 Dec
PMID:[Culture and differentiation of obligatory aerobic gram-negative rods from human material; a scheme for application in routine diagnosis (author's transl)]. 101 32

A chemically-defined medium was developed which supported growth of Streptococcus faecium and permitted synthesis of urease. This streptococcus cannot utilize ammonia and needs a complex medium, but its requirements are probably provided in the rumen. The specific activity of urease was inversely related to growth and in no medium was there high growth and high urease activity. Anaerobic culture and the presence of urea in the medium were essential for urease activity, but not for growth.
J Gen Microbiol 1976 Dec
PMID:A chemically-defined medium for the growth of a ureolytic strain of Streptococcus faecium. 103 71

Seven species of human T-mycoplasmas that grow in Fraction A and 20 mug urea/ml died when the urea was omitted. Two species would not grow in Fraction A broth containing 10 mug/urea/ml. The other five strains grew in broth containing 10 mug urea/ml and were adapted by serial passage in broth containing decreasing concentrations of urea to grow in broth containing 2.5 mug/ml urea, but not in broth containing 1.25 mug/ml. Therefore the minimal urea requirement is not the same for the growth of all strains of T-mycoplasmas. In exponential phase broth cultures, urease was detected only intracellularly, none being found in the medium.
Proc Soc Exp Biol Med 1975 Dec
PMID:The urea requirement and urease production of some human species of T-mycoplasmas. 120


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