pH‐Dependent Changes of 2,3‐Bisphosphoglycerate in Human Red Cells during Transitional and Steady States in vitro

Abstract

A systematic study of the pH-dependent changes in the range 6.6-7.4 of 2,3-bisphosphoglycerate and the adenine nucleotides was performed in the presence and absence of glucose during transitional and steady states. 2,3-Bisphosphoglycerate phosphatase [EC 3.1.3.15] breaks down 2,3-bisphosphoglycerate nearly independent of pH at a rate of 480 .mu.mol 2,3-bisphosphoglycerate .times. 1 cells-1 .times. h-1. 2,3-Bisphosphoglycerate mutase [EC 2.7.5.3] is almost completely inhibited below pH 6.9. An increased Km 2,3-bisphosphoglycerate is postulated. The 2,3-bisphosphoglycerate level in the presence of glucose reaches a pH-dependent steady state after about 18 h in keeping with theoretical predictions. The constancy of the adenine nucleotides in the presence of glucose regardless of the rate of glycolysis indicates a close coupling between ATP formation and breakdown. The decline of the sum of adenine nucleotides appears to be determined by the rate of AMP breakdown. The share of the 2,3-bisphosphoglycerate bypass in the steady state decreases from 24% at pH 7.4 to 12% at pH 7.04. The initially decreased glycolysis at low pH values increases in long-term experiments with lower 2,3-bisphosphoglycerate levels. The formation of pyruvate corresponds to the breakdown of 2,3-bisphosphoglycerate after consumption of an unknown reducing substance.