The S-conjugation rates of the free-reacting thiols present on each component of rat hemoglobin with 5,5-dithio-bis(2,2-nitrobenzoic acid) (DTNB) have been studied under a variety of conditions. On the basis of their reactivity with DTNB (0.5 mM), three classes of thiols have been defined as follows: fast reacting (fHbSH), with t( 1/4 ) <100 ms; slow reacting (sHbSH), with t( 1/4 ) 30-50 s; and very slow reacting (vsHbSH), with t( 1/4 ) 180-270 s. Under paraphysiological conditions, fHbSH (identified with Cys.125β(H3)) conjugates with DTNB 100 times faster than glutathione and ~4000 times more rapidly than (v)sHbSH (Cys-13α(A11) and Cys-93β(F9)). Such characteristics of fHbSH reactivity that are independent of the quaternary state of hemoglobin are mainly due to the following: (i) its low pK (~6.9, the cysteinyl anion being stabilized by a hydrogen bond with Ser-123β(H1)) and (ii) the large exposure to the solvent (as measured by analysis of a model of the molecular surface) and make these thiols the kinetically preferred groups in rat erythrocytes for S-conjugation. In addition, because of the high cellular concentration (8 mM, i.e. four times that of glutathione), fHSHs are expected to intercept damaging species in erythrocytes more efficiently than glutathione, thus adding a new physiopathological role (direct involvement in cellular strategies of antioxidant defense) to cysteinyl residues in proteins.

Rossi, R., Barra, D., Bellelli, A., Boumis, G., Canofeni, S., CHERUBINI DI SIMPLICIO, P., et al. (1998). Fast-reacting thiols in rat hemoglobins can intercept damaging species in erythrocytes more efficiently than glutathione. THE JOURNAL OF BIOLOGICAL CHEMISTRY, 273(30), 19198-19206 [10.1074/jbc.273.30.19198].

Fast-reacting thiols in rat hemoglobins can intercept damaging species in erythrocytes more efficiently than glutathione

ROSSI, RANIERI;CHERUBINI DI SIMPLICIO, PAOLO;
1998-01-01

Abstract

The S-conjugation rates of the free-reacting thiols present on each component of rat hemoglobin with 5,5-dithio-bis(2,2-nitrobenzoic acid) (DTNB) have been studied under a variety of conditions. On the basis of their reactivity with DTNB (0.5 mM), three classes of thiols have been defined as follows: fast reacting (fHbSH), with t( 1/4 ) <100 ms; slow reacting (sHbSH), with t( 1/4 ) 30-50 s; and very slow reacting (vsHbSH), with t( 1/4 ) 180-270 s. Under paraphysiological conditions, fHbSH (identified with Cys.125β(H3)) conjugates with DTNB 100 times faster than glutathione and ~4000 times more rapidly than (v)sHbSH (Cys-13α(A11) and Cys-93β(F9)). Such characteristics of fHbSH reactivity that are independent of the quaternary state of hemoglobin are mainly due to the following: (i) its low pK (~6.9, the cysteinyl anion being stabilized by a hydrogen bond with Ser-123β(H1)) and (ii) the large exposure to the solvent (as measured by analysis of a model of the molecular surface) and make these thiols the kinetically preferred groups in rat erythrocytes for S-conjugation. In addition, because of the high cellular concentration (8 mM, i.e. four times that of glutathione), fHSHs are expected to intercept damaging species in erythrocytes more efficiently than glutathione, thus adding a new physiopathological role (direct involvement in cellular strategies of antioxidant defense) to cysteinyl residues in proteins.
Rossi, R., Barra, D., Bellelli, A., Boumis, G., Canofeni, S., CHERUBINI DI SIMPLICIO, P., et al. (1998). Fast-reacting thiols in rat hemoglobins can intercept damaging species in erythrocytes more efficiently than glutathione. THE JOURNAL OF BIOLOGICAL CHEMISTRY, 273(30), 19198-19206 [10.1074/jbc.273.30.19198].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11365/437543