6 X-Ray Diffraction Studies of Heparin Conformation 1
Downloaded by FUDAN UNIV on March 28, 2017 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0048.ch006
I. A. NIEDUSZYNSKI, Κ. H. GARDNER, and E. D. T. ATKINS H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, U.K.
Introduction, H e p a r i n is a s u l p h a t e d p o l y s a c c h a r i d e which o c c u r s as intra-cellular p a c k e t s o f m a t e r i a l in mast cells and has a f u n c t i o n in fat-clearing and as a blood anti-coagulant. In this latter role, h e p a r i n f i n d s g r e a t application in m e d i c i n e and is isolated on a commercial s c a l e . The d e t a i l e d c h e m i c a l s t r u c t u r e o f h e p a r i n is still under investigation, b u t it is believed t o have a g l y c o s a m i n o - g l y c u r o n a n backbone (-H-U-) where H is g e n e r a l l y 2-deoxy-2-sulphamino-fl-D-glucose-6-sulphate and U is m a i n l y 2 - s u l p h a t e d ^ ( - L - i d u r o n i c a c i d b u t a l s o c o n t a i n s some ß-D-glucuronic a c i d . H e p a r i n s g e n e r a l l y have 2-3 s u l p h a t e e s t e r groups p e r d i s a c c h a r i d e and a small p r o p o r t i o n o f N-acetyl groups. S i n c e t h e known f u n c t i o n s o f h e p a r i n a r e m e d i a t e d by specific b i n d i n g t o p r o t e i n s such as l i p o p r o t e i n lipase (1) and t h e v a r i o u s b l o o d c o a g u l a t i o n f a c t o r s (2) a knowledge o f t h e detailed shape o f t h e m o l e c u l e is o f g r e a t i m p o r t a n c e . T h i s p o i n t may be emphasized by comparison (3,4) o f t h e a n t i c o a g u l a n t a c t i v i t i e s o f h e p a r i n (about 160 IU/mg.) and c e r t a i n heparan s u l p h a t e s ( e . g . about 16 IU/mg.); t h e l a t t e r m o l e c u l e s b e i n g c h e m i c a l l y s i m i l a r t o h e p a r i n and d i f f e r i n g p r i n c i p a l l y i n having a higher p r o p o r t i o n o f -D-gluc u r o n i c a c i d and one s u l p h a t e e s t e r group fewer p e r disaccharide. The p r i n c i p a l p r o b l e m i n d e t e r m i n i n g t h e shape o f the h e p a r i n m o l e c u l e r e s i d u e s i n t h e c o n f o r m a t i o n o f t h e o { - L - i d u r o n a t e r e s i d u e , s i n c e t h e hexosamine resi due i s e x p e c t e d t o e x i s t i n t h e n o r m a l 4 ^ c h a i r i n which a l l o f t h e b u l k y s u b s t i t u e n t s would be e q u a t o r i a l l y disposed. In the sulphatedo(-L-iduronate residue n
1Current address: D e p t . B i o l . Sciences, U n i v e r s i t y of Lancaster, L a n c a s t e r LA1 4 Y Q , Lancashire, E n g l a n d .
73
Arthur; Cellulose Chemistry and Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
74
CELLULOSE
CHEMISTRY
A N D
TECHNOLOGY
Downloaded by FUDAN UNIV on March 28, 2017 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0048.ch006
4
( F i g . 2 ) , however, t h e normal C j c h a i r would r e q u i r e an a x i a l c a r b o x y l group and t h e a l t e r n a t i v e ^ 4 c h a i r r e q u i r e s a x i a l s u l p h a t e and l i n k a g e p o s i t i o n s . It i s c o n s e q u e n t l y d i f f i c u l t t o choose between t h e s e two r e s i d u e c o n f o r m e r s and o t h e r forms a l s o need t o be considered. R e c e n t l y , X-ray f i b r e d i f f r a c t i o n p a t t e r n s have been o b t a i n e d from p i g mucosal h e p a r i n ( 5 J and macrom o l e c u l a r h e p a r i n from r a t s k i n s (j6) and t h e s e g i v e the f i r s t information o f the molecular repeat d i s t a n c e s i n h e p a r i n . On t h e b a s i s o f t h e o b s e r v e d t e t r a s a c c h a r i d e r e p e a t i n g d i s t a n c e t h e s e p a t t e r n s have been i n t e r p r e t e d as f a v o u r i n g t h e ^ 4 r e s i d u e c o n f o r m a t i o n whose a x i a l p r o j e c t i o n i s s h o r t e r r a t h e r than t h e conformation f o r o(-L-iduronate. In t h i s paper a l l o f t h e 0.3 nm. X-ray d a t a i s u s e d i n a more comprehensive study o f t h e ^ - L - i d u r o n ate residue conformation i n heparin. The o(-L-Iduronate R e s i d u e . The ) and NMR d a t a ( 11) has f a v o u r e d t h e ^ 4 over t h e ^C^ c o n f o r m e r , but no d e f i n i t i v e statement has been made e l i m i n a t i n g o t h e r p o s s i b l e conformers. In p r i n c i p l e , p y r a n o s e s may adopt any o f 26 s t a n d a r d r e s i d u e c o n f o r m a t i o n s ( s e e (12) f o r a comprehensive nomenclature system). These i n c l u d e 2 c h a i r s , 6 b o a t s , 6 skew-boats and 12 h a l f - c h a i r s . A molecular model o f 2 - s u l p h a t e d
