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1

Competitive inhibitors of free and chitosan-immobilized urease

100%
Zaborska W.
Acta Biochimica Polonica
|
1995
|
tom 42
|
nr 1
The influence of four inhibitors: boric acid, thioglycolic acid, sodium fluoride and acetohydroxamic acid on the activity of urease, both in the native form and immo­bilized covalently on glutaraldehyde-pretTeated chitosan membrane, was studied. Urea hydrolysis was carried out in phosphate buffer, pH 7, at 25°C at urea concen­tration of 50 mM. The immobilized urease was more resistant than the native one to the action of all the investigated inhibitors, except boric acid. This property of the enzyme offers a possibility of its practical application.
2
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A spectrophotometric assay for total garlic thiosulfinates content. Kinetic aspects of reaction with chromogenic thiols

63%
Olech Z., Zaborska W.
Polish Journal of Food and Nutrition Sciences
|
2012
|
tom 62
|
nr 1
Garlic (Allium sativum) is a plant known for its antimicrobial, antithrombotic and antiatherosclerotic properties. Those features are attributed to thiosulfi nates, compounds formed in an enzymatic reaction occurring during garlic cloves crashing. A spectrophotometric method for the determination of thiosulfi nate concentration in garlic extracts and supplements was proposed. It is based on reactions between thiosulfi nates and selected chromogenic thiol compounds: 2-mercaptopyridine (2-MP), 4-mercaptopyridine (4-MP), 1-oxide-2-mercaptopyridine (MPO), 2-mercaptopyrimidine (MPM) and 2-nitro-5-thiobenzoic acid (NTB). Then kinetics of the reactions was studied. Rate constants and orders were determined. All reactions are fi rst order with respect to the thiol and fi rst order with respect to TS so the reactions of all tested thiols with garlic TS run in accordance with second order kinetics. Reaction rates vary among the thiol compounds: the constant rates differ from 6.7 (mol/L)-1.min-1 for 2-MP to 1129 (mol/L)-1.min-1 for NTB. Knowledge of the kinetic equation for the reactions and measurements of the initial rates allowed determining thiosulfi nate contents in garlic extracts and supplements.
3

Effect of thiosulphinates contained in garlic extract on growth, proton fluxes and membrane potential in maize (Zea mays L.) coleoptile segments

51%
Polak M., Zaborska W., Tukaj Z., Karcz W.
Acta Physiologiae Plantarum
|
2012
|
tom 34
|
nr 1
The effect of thiosulphinates contained in garlic extract (GE) on endogenous growth, growth in the presence of either indoleacetic acid (IAA) or fusicoccin (FC), and proton extrusion in maize coleoptile segments were studied. In addition, membrane potential changes at some GE dilutions and the protective effect of dithiothreitol (DTT) against GE toxicity were also determined. It was found that GE at almost all dilutions studied, when added to the incubation medium inhibited endogenous growth as well as growth in the presence of either IAA or FC. Simultaneous measurements of growth and external pH indicated that the administration of GE resulted in a complex change in the pH of the external medium; after an initial transient acidification, pH increased and reached the maximal value followed by a gradual decrease of medium pH. When IAA or FC was added after preincubation of the segments in the presence of GE the changes in medium pH were not significantly different from these obtained with GE only. If the coleoptile segments were first preincubated with GE and subsequently GE was removed, the addition of IAA induced strong growth and medium acidification. Dithiothreitol added together with GE neutralized the toxic effect of GE on growth of coleoptile segments incubated in the presence of IAA. The addition of GE to the control medium caused a depolarization of the membrane potential, the value of witch depended on GE dilution. These results indicate that the toxic effect of GE on growth of plant cells might be caused by disruption of the catalytic function of the plasma membrane H⁺-ATPase on formation of the disulfide bonds.
4

The enthalpimetric determination of inhibition constants for the inhibition of urease by acetohydroxamic acid

51%
Zaborska W., Leszko M., Kot M., Juszkiewicz A.
Acta Biochimica Polonica
|
1997
|
tom 44
|
nr 1
The effect of concentration of acetohydroxamic acid (AHA) on inhibition of jack bean urease in phosphate buffer, pH 7.0, at 25°C, was studied. The meas­urements were performed at urease concentration of 2.5 mg/100 cm3 for con­centrations of urea and AHA ranging in the range of 2-50 mmol dm-3 and 0.25-10 mmol dm-3, respectively. The reactions were monitored by two techniques: analytical and enthalpimetric. For the analytical technique the growth of ammonia concentration in the course of the reaction was determined. From the recorded progress curves the following parameters were calculated for each inhibitor concentration: the initial reaction rate, the steady-state rate and the inversion constant. From these parameters the inhibition constants of the initial and steady-state stages of the reaction, K\ and K\y were calculated. The former constant did not change whereas the latter one proved to decrease quickly with an increase in inhibitor concentration. This behaviour resulted from the fact that the inactive complex EI* was not a product of internal inversion but was formed in the reaction: — 2/3I + EI —> (EI • — 2/3I)*. The disso3ciation constant of this complex is equal to about 0.3 x 10-3 (mol dm-3)2/3.
5

Ureolytic activity of Nitellopsis obtusa [Characeae]

51%
Karcz W., Krajewska B., Zaborska W.
Acta Physiologiae Plantarum
|
2001
|
tom 23
|
nr 3
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