Additional factors influencing enzyme responses to the adenylate energy charge.

Energy charge responses of yeast hexokinase, rabbit muscle pyruvate kinase, soluble rat brain hexokinase, and rabbit muscle phosphofructokinase were observed. Several additional factors that were shown to influence markedly the sensitivity of these enzyme responses to the adenylate energy charge include pH, total adenylate concentration, levels of non-adenylate reaction products, and non-adenine nucleotides. Computed response curves also indicated that the value of the adenylate kinase mass action ratio can also affect enzyme responses to the energy charge. Other simulations suggest that there is no apparent theoretical basis for energy charge stabilization in the range of 0.75 to 0.90. Finally, it is suggested that in vitro energy charge responses may be quite misleading, depending upon the relative influence of a number of experimentally adjusted factors.