ABSTRACT
In cellular and subcellular biology, which is a science describing phenomena proceeding in 99% of cases in an aqueous solution, pH can be considered as one of the essential intensive parameters, much like temperature or viscosity. Every cell and organelle, and every type of body fluid is characterized by a narrow range of pH values within which it can only function properly. The greatest number of measurements have been done on mammalian cells, particularly muscle and nerve cells and on erythrocytes. The molecular basis of the existence of an optimum pH value for an enzyme is now generally believed to be the correct protonation of the enzyme-active site for it to be functional. Like enzymes, all specific transport systems are subject to catalytic pH effects, and pH optima of transport reactions are commonly reported in the literature, particularly for transport by unicellular organisms where the external pH can be varied without detrimental effects on the organism.
