 Though the reaction may seem too uphill to occur, it is of note that under physiological conditions, the ΔG of the reaction falls to close to or below zero.For example, the ΔG of this reaction under physiological conditions in erythrocytes is -0.23 kJ/mol.Aldolase B is a homotetrameric enzyme, composed of four subunits with molecular weights of 36 kDa with local 222 symmetry.