The chemistry of connective tissues. 6. The constitution of the chondroitin sulphate–protein complex in cartilage

Abstract

EQUILIBRIA OF GLUCOSE PHOSPHATE HYDROLYSIS 15 None of the equilibrium concentrations discussed here have been corrected for variation of the activity coefficients from unity, but the absence of any apparent dependence of the constants on reactant concentrations suggests that the apparent free energies of hydrolysis calculated here differ little from the true free energies of hydrolysis.SUMMIARY 1. Specific enzymic methods were used to estimate the equilibrium concentrations of (cx + fi)-D-glucose 6-phosphate and of aC-D-glucose 1-phos- phate in the products of the reaction catalysed by muscle phosphoglucomutase at pH 7-0 and 250 with 25mM-Mg2+.The apparent equilibrium constant, [(c + f)-D-glucose 6-phosphate]/[oc-D-glu- cose 1-phosphate], was 17 + 2 and the apparent free energy of phosphoryl transfer (AG') was -17 + 041 kcal./mole.2. Specific enzymic methods were also used to estimate the equilibrium concentrations of (ac+ ,B)- D-glucose and of (aC+,B)-D-glucose 6-phosphate in the products of hydrolysis of glucose 6-phosphate catalysedby intestinalalkalinephosphatase.Orthophosphate was estimnated as phosphomolybdate.At pH 7*0 with 5 mM-Mg2+ the apparent equi- libriurm constant [(aC+,)-D-glucose] [orthophos- phate]/[(ac + ,B)-D-glucose 6-phosphate] was 260 ± 50, and the apparent free energy of hydrolysis was -3-3 0-1 kcal./mole.There was little change in the apparent equilibrium constant with increasing concentration of Mg2+ ions between 0 and 5 mm at pH 7-0. 3. From these results, the apparent free energy of hydrolysis of aX-D-glucose 1-phosphate is -5-0 kcal./mole at pH 7-0 in the presence of Mg2+ ions.We wish to thank Professor S. Angyal, University of New South Wales, for valuable advice on the effect of con- figuration on thermodynamic properties in hexose phos- phates.