Catalytic influence of heparin on auramine O hydrolysis: A basis for differentiating heparin from other glycosaminoglycans based on its properties as a polyelectrolyte

Abstract

SynopsisThe basis for heparin's ability to accelerate the conversion of auramine 0 (AuO) to Michlers ketone [P. Band & A. Lukton (1982) A n d . Biochem. 120, [19][20][21][22][23][24] is here explained in terms of well-known polyelectrolyte phenomena. Acceleration of this acidcatalyzed hydrolysis appears to be due to colocalization of the cationic dye and hydronium ion within the microenvironment of heparin's electrostatic domain. The dependence of reaction rate on polymer, dye, and hydronium ion concentration, ionic strength, and various ratios of these parameters is consistent with what others have observed for polyelectrolyte catalysts. Dextran sulfate, polyvinyl sulfate, and polyanethole sulfonate likewise accelerate this reaction, thus precluding any explanation of the catalysis in terms of a specific catalytic site. A striking aspect about the polyanionAuO system is the inability of all other natural glycosaminoglycans tested to catalyze this reaction, despite their analogous polyanionic nature. Manning's limiting laws describing counterion condensation in polyelectrolyte solutions provide a simple context within which to interpret these results. Calculation of the structural linear charge density parameter, e, based on analytically determined sulfate-to-hexosamine ratios, reveals that heparin is unique among the glycosaminoglycans in possessing an 5 value greater than unity under the conditions described. Thus, heparin's differential ability to catalyze AuO hydrolysis is a reflection of the fact that only heparin is sulfated to an extent great enough to maintain 5 > 1, even when the negative charge of carboxylate groups is neutralized. It is proposed that this distinction may be important to the unique biochemical attributes of heparin and that such considerations may prove useful in establishing structurefunction relationships when comparing different glycosaminoglycan classes.

Acceleration of the mercury-induced aquation of bromopentammine Co(III) by naturally occurring glycosaminoglycans

“…Clearly the GAGs are anionic polyelectrolytes with significant axial charge densities (vide infra). These vary from 5 = 0.7 for hyaluronic acid to 2 < 5 < 3.5 for various heparins (14,15, and present work).…”

“…In large part this is due to a lack of understanding of the very functions for which explanations are sought, and the teleological approach of deducing functions from polyelectrolyte properties has been favoured by some (14,17). This potentially productive approach requires a detailed understanding of polyion-counterion interactions, and some important steps in this direction have been taken.…”

“…For example, with a 6-mV difference between +[heparin] and +[ChS(A)], eq. [14] predicts a difference in maximum rates of nearly 12 times.…”

“…The mean repeat lengths for the fractionated lung heparan sulfates (HS-I and HS-11) have not been reported. However, if we assume both to have a disaccharide length of 0.93 nm, intermediate between heparin and the chondroitins, as reported for unfractionated heparan sulfate (14), then charge densities intermediate between heparin and the chondroitins are also calculated. The order of 5 values for all polymers follows their order of elution from the poly-L-lysine column, as expected (Fig.…”