Influence of natural and synthetic humic substances on the activity of urease   总被引：1，自引：0，他引：1  

D. VAUGHAN  B. G. ORD 《European Journal of Soil Science》1991,42(1):17-23

The activity of a purified urease, obtained from Bacillus pasteurii, was inhibited by humic and fulvic acids obtained from an agricultural soil. Enzyme kinetic studies showed that the humic substances affected the affinity of the enzyme for its substrate (K_m) and the maximum velocity of the reaction (V_max). The V_max was inhibited to the same extent by both humic (HA) and fulvic (FA) acids, the precise effect depending on the pH and concentration of humic substance. At pH 4.0, HA concentrations of 25 pg cm^?3 and 10 μg cm^?3 inhibited the V_max by 38.5% and 20% respectively. HA and FA had similar effects on the K_m but in this case the lowering of the affinity of the enzyme for its substrate was not concentration dependent in the range 0–25 μg cm^?3 of humic substance. Typically, the affinity was decreased from a K_M of 50 mM in the control to 67 mM in the presence of HA and FA. The effects were not due primarily to the ash or N contents of the humic substances because de-ashed humic acid and synthetic model humic (made from catechol, guaiacol, pyrogallol, resorcinol and protocatechuic acid) and fulvic acid (made from polymaleic acid), containing virtually no ash or N, were equally as effective. The effect was not related to the phenolic monomers which, before polymerization, had no effect on urease activity.  相似文献   

Spectroscopic Observation of the Formyl Cation in a Condensed Phase     

de Rege PJF  JA Gladysz  IT Horvath 《Science (New York, N.Y.)》1997,276(5313):776-779

The formyl cation, HCO+, has long been believed to be an important intermediate in the chemistry of carbon monoxide (CO) in acidic environments, but its spectroscopic observation in solution has been elusive. This species was generated by the reaction of CO with the liquid superacid hydrofluoric acid-antimony pentafluoride (HF-SbF5) under pressure and was observed by nuclear magnetic resonance and infrared spectroscopy. Equilibria between CO in the gas phase, CO dissolved in HF-SbF5, the SbF5 adduct of formyl fluoride, and HCO+ associated with several equilibrating anions of the type [SbxF5x+1]- are proposed to describe the system.  相似文献   

Virus isolated from inclusion conjunctivitis of newborn (inclusion blennorrhea)     

HANNA L  ZICHOSCH J  JAWETZ E  VAUGHAN DG  THYGESON P 《Science (New York, N.Y.)》1960,132(3440):1660-1661

An infant developed acute conjunctivitis 7 days after birth. Smears of the mucopurulent discharge contained many typical elementary-body inclusions. From conjunctival scrapings a virus resembling trachoma was grown in eggs. When instilled into monkey eyes, it produced an acute conjuctivitis resembling the human disease. Nine other patients with inclusion conjunctivitis of similar intensity failed to yield viruses.  相似文献   

Preparation of tritiated proteins by the Wilzbach method     

STEINBERG D  VAUGHAN M  ANFINSEN CB  GORRY J 《Science (New York, N.Y.)》1957,126(3271):447-448

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In vitro studies on the action of sulfonamide hypoglycemic agents     

VAUGHAN M 《Science (New York, N.Y.)》1956,123(3203):885-886

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Predatory Dinosaurs from the Sahara and Late Cretaceous Faunal Differentiation     

PC Sereno  DB Dutheil  M Iarochene  HCE Larsson  GH Lyon  PM Magwene  CA Sidor  DJ Varricchio  JA Wilson 《Science (New York, N.Y.)》1996,272(5264):986-991

Late Cretaceous (Cenomanian) fossils discovered in the Kem Kem region of Morocco include large predatory dinosaurs that inhabited Africa as it drifted into geographic isolation. One, represented by a skull approximately 1.6 meters in length, is an advanced allosauroid referable to the African genus Carcharodontosaurus. Another, represented by a partial skeleton with slender proportions, is a new basal coelurosaur closely resembling the Egyptian genus Bahariasaurus. Comparisons with Cretaceous theropods from other continents reveal a previously unrecognized global radiation of carcharodontosaurid predators. Substantial geographic differentiation of dinosaurian faunas in response to continental drift appears to have arisen abruptly at the beginning of the Late Cretaceous.  相似文献   

Fenthion poisoning of native birds in southern Queensland     

RA McKENZIE  AEL LANHAM  JD TAYLOR  JA GIBSON  RJ PIERCE 《Australian veterinary journal》1996,74(4):321-323

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Artificial Insemination in Dogs     

JA Rodger 《Australian veterinary journal》1993,70(12):462-463

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Chronic renal failure and urolithiasis in a 2-years-old colt     

JA LAING  AL RAISIS  RJ RAWLINSON  AC SMALL 《Australian veterinary journal》1992,69(8):199-200

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4 THE EFFECTS OF EXERCISE AND INJURY ON CHONDROITIN SULFATE AND KERATAN SULFATE CONTENT IN EQUINE SYNOVIAL FLUID.     

MP  Brown  AHK Plaas  JD Sandy  JA Hernandez  KA Merritt  . 《Veterinary surgery : VS》2003,32(6):599-599

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