Abstract

The reactivities of the sulphydryl groups of minor component of duck hemoglobin with 5,5¹-dithiobis-(2-nitrobenzoic acid), DTNB, in the presence of inositol hexakisphosphate (inositol-P₆) have been studied.  The reaction has been monitored as a function of pH (pH 7.0 – 9.0) and at ionic strength of 50 mmolL^-1.  The carbonmonoxy and aquomet derivatives were used for the study. Biphasic time courses were obtained under all experimental conditions and the two kinetic phases were well separated along the time axis. From the observed pseudo-first order rate constants, k_obs, the apparent second-order rate constants, k_app, were calculated.  Inositol-P₆ reduced the rates of all reactions for the two derivatives for both CysF9(93)β and CysB5(23)β. The reaction of CysF9(93)β gave an increase of 0.88 unit of pK_a for the aquomet derivative but a decrease of 0.40 unit of pK_a for the carbonmonoxy derivative. The salt-bridge formed between HisHC3 and AspFG1 is more strengthened by inositol-P₆ in aquomet than in carbonmonoxy derivative.

Key words: Duck, hemoglobin, sulphydryl, inositol-P₆.