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Kinetic studies on the oxidation of nitrite by horseradish peroxidase and lactoperoxidase

100%

Gębicka L.

Acta Biochimica Polonica

1999

vol. 46

issue 4

919-927

The reaction of nitrite (NO-_2) with horseradish peroxidase and lactoperoxidase was studied. Sequential mixing sopped-flow measeruments gave the following values for the rate constants of the reaction of nitrite with compounds II (oxoferryl heme intermediates) of horseradish peroxidase and lactoperoxidase at pH 7.0, 13.3 ± 0.07 mol^{-1}dm^3s^{-1} and 3.5 ± 0.05 · 10^4mol^{-1}dm^3s^{-1}, respectively. Nitrite, at neutral pH, influenced measurements of activity of lactoperoxidase with typical substrates like 2,2'-azino-bis[ethyl-benzothiazoline-(6)-sulphonic acid] (ABTS), guaiacol or thiocyanate (SCN-). The rate of ABTS and guaiacol oxidation increased linearly with nitrite concentration up to 2.5-5 mmol dm^{-3}. On the other hand, two-electron SCN- oxidation was inhibited in the presence od nitrite. Thus, nitrite competed with the investigated substrates of lactoperoxidase. The intermediate, most probably nitrogen dioxide (*NO_2), reacted more rapidly with ABTS or guaiacol than did lactoperoxidase compound II. It did not, however, effectively oxidize SCN- to OSCN-. NO-_2 did not influence the activity measurements of horseradish peroxidase by ABTS or guaiacol method.

Insight into the kinetics and the mode of the interaction between smooth muscle calponin and F-actin.

88%

Kołakowski J., Dąbrowska R.

Acta Biochimica Polonica

2002

vol. 49

issue 2

471-479

Kinetics of the smooth muscle calponin-F-actin interaction was studied by stopped- flow measurements of light scattering and fluorescence intensity of pyrene-labelled F-actin. The intensity and character of the changes in light scattering, and thus the mode of calponin binding to actin filaments leading to changes in their shape and bundling, depend on the molar ratio of the two proteins. Parallel measurements of pyrene-fluorescence quenching upon calponin binding revealed that intrinsic conformational changes in actin filaments are delayed relative to the binding process and are not markedly influenced by the mode of calponin binding. Bundling of actin filaments by calponin was not correlated with fluorescence changes and thus with alterations in the structure of actin filaments.

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2 Acta Biochimica Polonica

1 2002

1 1999

1 Dąbrowska R.

1 Gębicka L.

1 Kołakowski J.

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Kinetic studies on the oxidation of nitrite by horseradish peroxidase and lactoperoxidase

Insight into the kinetics and the mode of the interaction between smooth muscle calponin and F-actin.