Functional analysis of Carp hemoglobin according to the theories of Adair; of Monod, Wyman & Changeux (MWC), and of Koshland, Némethy & Filmer (KNF)

Abstract

The p r o p e r t i e s o f Carp hemoglob in ( C y p r i n u s c a r p i o ) add a new d imens ion to the f u n c t i o n a l v e r s a t i l i t y o f the hemoglob in molec u l e . The a f f i n i t y o f Carp hemoglob in f o r oxygen shows an extreme pH dependence, 160 t imes h i g h e r at a l k a l i n e pH than at ac id pH. In o rde r to ana lyse p o s s i b l e f u n c t i o n a l mechanisms o f Carp hemog lob in , p r e c i s e e q u i l i b r i a were measured from approx i m a t e l y I% to 99% oxygen s a t u r a t i o n at 15~ in b i s t r i s b u f f e r and in phosphate b u f f e r in the presence and absence o f P 6 i n o s i t o l ( I H P ) ( 1 ) . A d a i r c o n s t a n t s , k i , (2] were e s t i m a t e d by nonl i n e a r l e a s t square f i t o f H i l l pTo ts . Parameters of the Monod, Wyman & Changeux (MWC) model (3 ] were es t ima ted by a s i m i l a r n o n l i n e a r l e a s t square p rocedure and by i t e r a t e d computer c a l c u l a t i o n s from the Ada i r pa ramete rs . The parameters o f the s i m p l e , s e q u e n t i a l model o f Kosh land , N~methy & F i l m e r (KNF) 14) were c a l c u l a t e d from the A d a i r pa ramete rs . From the A d a i r c o n s t a n t s , one can conc lude t h a t Carp hemog lob in , in the coo p e r a t i v e reg ime, undergoes an a l l o s t e r i c t r a n s i t i o n a f t e r oxy gena t i on o f the t h i r d heme; l o w e r i n g of c o o p e r a t i v i t y by changes in pH seems to s h i f t c o n f o r m a t i o n a l t r a n s i t i o n s to e a r l i e r s t a ges o f o x y g e n a t i o n . The MWC parameters o f KR, ~ , and L were found to be 8.2 mmHg-1, 1.3 x 10-2 and 4.2 x 106, r e s p e c t i v e l y , at pH 7.2 (maximal c o o p e r a t i v i t y in phosphate b u f f e r ) . Changes in pH in e i t h e r d i r e c t i o n i nc rease the va lues o f K R and L, and d~c~ease the va lue o f c. Larqe va lues o f L at reduced coopera~ l V l ~ y are un reasonab l~ i n ~he c o n t e x t o f t h i s moael. The s i m p l e , s e q u e n t i a l KNF model , as i n t e r p r e t e d here , seems to p r e d i c t a symmetry conserved mode of a c t i o n in r eg ions o f h i g h , p o s i t i v e c o o p e r a t i v i t y , and a symmetry non-conserved mode o f a c t i o n in r eg ions o f low, non , o r n e g a t i v e c o o p e r a t i v i t y . T h e r e f o r e , when reg ions o f h i g h , p o s i t i v e c o o p e r a t i v i t y are enc o u n t e r e d , an a lmost conce r ted c o n f o r m a t i o n a l t r a n s i t i o n occurs upon l i g a n d b i n d i n g . In t h i s case, the KNF model e x t r a p o l a t e s to the MWC model f o r a l l i n t e n t s and purposes .

DOI: 10.1007/BF00647519

Cite this paper

@article{Mayo2004FunctionalAO, title={Functional analysis of Carp hemoglobin according to the theories of Adair; of Monod, Wyman & Changeux (MWC), and of Koshland, N{\'e}methy & Filmer (KNF)}, author={Kevin H . Mayo}, journal={Biophysics of structure and mechanism}, year={2004}, volume={6}, pages={46-46} }