Tertiary conformational transition in sheep hemoglobins induced by reaction with 5,5 -dithiobis(2-nitrobenzoate) and by binding of inositol hexakisphosphate.
We have determined the second-order reverse rate constant, k(R), for the reaction of 5,5 -dithiobis(2-nitrobenzoate) - DTNB - with sheep hemoglobins as a function of pH from values of the second-order forward rate constant, k(F), and the equilibrium constant, K(equ), at 25 degrees C: k(R)=k(F)K(equ). We demonstrate that (i) inositol hexakisphosphate (inositol-P(6)) decreases k(F) and k(R) by increasing K(rt), the rright harpoon over left harpoont tertiary conformation transition constant; (ii) the conformation favored for both the forward and reverse reactions is the r conformation. For stripped hemoglobin we obtain from the k(F) data a t isomer population of 34.6% (+/-14) prior to reaction with DTNB; from the k(R) data we calculate a t isomer population of 44.8% (+/-4) following reaction with DTNB. In the presence of inositol-P(6) the latter value is increased to 79.5% (+/-2). These results demonstrate that an allosteric transition occurs on reaction with DTNB and on inositol-P(6) binding.
Okonjo
Kehinde Onwochei
KO
Department of Chemistry, Covenant University, Ota, Ogun State, Nigeria. kehindeokonjo@gmail.com
Adeogun
Idowu A
IA
Babalola
J Oyebamiji
JO
D000818:Animals; D004228:Dithionitrobenzoic Acid / Q000737:chemistry* / Q000494:pharmacology*; D006454:Hemoglobins / Q000737:chemistry* / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010833:Phytic Acid / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000187:drug effects; D012756:Sheep
D006454:Hemoglobins; D010833:Phytic Acid; D004228:Dithionitrobenzoic Acid