African Journal of
Biotechnology

  • Abbreviation: Afr. J. Biotechnol.
  • Language: English
  • ISSN: 1684-5315
  • DOI: 10.5897/AJB
  • Start Year: 2002
  • Published Articles: 12496

Full Length Research Paper

The reactivity of CysF9[93]β sulphydryl group of des-HisHC3[146]β human haemoglobin A

J. Oyebamiji Babalola1*, N. Adesola Babarinde2 and A. Idowu Adeogun3
1Department of Chemistry, University of Ibadan, Ibadan, Nigeria. 2Department of Chemical Sciences, Olabisi Onabanjo University, Ago Iwoye, Ogun, Nigeria. 3Department of Chemistry, University of Agriculture, Abeokuta, Nigeria.
Email: [email protected]

  •  Accepted: 05 September 2011
  •  Published: 31 October 2011

Abstract

The pH dependence of the second order rate constant of the reaction of 5,5′-dithiobis(2-nitrobenzoate) (DTNB) with CysF9[93]β sulphydryl group of human haemoglobin A at 50 mmol dm-3 is complex. The removal of the terminal HisHC3[146]β of haemoglobin A by enzymatic cleavage with carboxypeptidase A breaks the salt bridge between HisHC3[146]β and AspFG1[94]β and reduces the strain on CysF9[93]β sulphydryl group. The pH dependence profiles of the second order rate constant for the reaction of DTNB with CysF9[93]β sulphydryl group of the modified haemoglobin A derivatives at 50 mmol dm-3 became simple with significant reduction in the reaction rates contrary to expectations. The implication is that CysF9[93]β becomes occluded and hence less reactive. The mean pKas of the ionizable groups linked to the reactivity of CysF9[93]β sulphydryl group of des-HisHC3[146]β human haemoglobin A were 5.52 ± 0.01 and 8.29 ± 0.1. These values are assigned to HisH21[143]β and CysF9[93]β amino acid residues, respectively.

 

Key words: Haemoglobin, CysF9[93]β, carboxypeptidase A, 5,5′-dithiobis(2-nitrobenzoate), salt bridge.