A simple novel method for determination of an inhibition constant by isothermal titration microcalorimetry. The effect of fluoride ion on urease

Inhibition of β-Amylase Activity by Calcium, Magnesium and Zinc Ions Determined by Spectrophotometry and Isothermal Titration Calorimetry

The inhibition effect of metal ions on beta amylase activity was studied. The inhibitor-binding constant (Ki) was determined by spectrophotometric and isothermal titration calorimetric (ITC) methods. The binding of calcium, magnesium and zinc ion as inhibitors at the active site of barley beta amylase was studied at pH = 4.8 (sodium acetate 16 mM) and T = 300K. The Ki and enthalpy of binding for calcium (13.4, 13.1 mM and -14.3 kJ/mol), magnesium (18.6, 17.8mM and -17.7 kJ/mol) and zinc (17.5, 17.7 mM and -20.0 kJ/mol) were found by spectrophotometric and ITC methods respectively.

Weak activity of haloalkane dehalogenase LinB with 1,2,3-trichloropropane revealed by X-Ray crystallography and microcalorimetry

1,2,3-Trichloropropane (TCP) is a highly toxic and recalcitrant compound. Haloalkane dehalogenases are bacterial enzymes that catalyze the cleavage of a carbon-halogen bond in a wide range of organic halogenated compounds. Haloalkane dehalogenase LinB from Sphingobium japonicum UT26 has, for a long time, been considered inactive with TCP, since the reaction cannot be easily detected by conventional analytical methods. Here we demonstrate detection of the weak activity (k(cat) = 0.005 s(-1)) of LinB with TCP using X-ray crystallography and microcalorimetry. This observation makes LinB a useful starting material for the development of a new biocatalyst toward TCP by protein engineering. Microcalorimetry is proposed to be a universal method for the detection of weak enzymatic activities. Detection of these activities is becoming increasingly important for engineering novel biocatalysts using the scaffolds of proteins with promiscuous activities.

Inhibition of soybean urease by triketone oximes

Competitive inhibition of soybean urease by 15 triketone oximes has been studied at 36 degrees C in aqueous solution (pH 4.95). The studied oximes are supposed chelators for the nickel atom in the urease metallocenter. The inhibition constants of urea hydrolysis (K(i)) varied in the range 2.7-248 microM depending on the oxime structure. Analysis of this dependency demonstrates that the optimal inhibitor is the one containing carbonyl group in position 1 of the cycle, the ethoxyimino group and alkyl residue in the substituent in position 2, as well as the methoxycarbonyl group in position 4 of the cycle.

Binding Properties of Adenosine Deaminase Interacted with Theophylline

Thermodynamic studies were carried out to evaluate the binding of theophylline on adenosine deaminase (ADA) in 50 mM sodium phosphate buffer pH 7.5, at 300 K, using isothermal titration calorimetry (ITC). A simple method for determination of binding isotherm in the drug--ADA interaction was applied using ITC data. ADA has two binding sites for theophylline, which show positive cooperativity in its sites. The intrinsic association equilibrium constants are 6 and 52 mM(-1) in the first and second binding sites, respectively. Hence, occupation of the first site has produced an appreciable enhancement by 8.7 of the binding affinity of the second site. The molar enthalpies of binding are -12.2 and -14.9 kJ/mol in the first and second binding sites, respectively.

A new mechanism of action of fluoride on streptococci

Addition of fluoride to the growth medium of Streptococcus sobrinus resulted in a loss of glucan-binding lectin activity. Upon removal of fluoride, the bacteria regained their ability to bind glucan in about one generation. Chloramphenicol prevented recovery of ability to produce the lectin, showing the requirement for protein synthesis. Fluoride also caused a significant reduction in the tendency of the streptococci to form chains of cells, although the spent medium from fluoride-containing growth media did not dechain control cells. The fluoride thus does not activate autolytic enzymes. Importantly, 2-D electrophoresis and SDS-PAGE revealed several proteins were synthesized in the presence of fluoride that were not synthesized in its absence. It seems possible that fluoride places a stress on the bacteria, causing the synthesis of proteins that may play a role in protecting the cells against the stress. Numerous stress proteins are known for bacteria, including those resulting from heat, enzymes and osmotic shocks. The ability of fluoride to cause loss of glucan-binding may be related to its reported beneficial effects on oral health.