Proteins pi values

The generation of lactic acid through glycolysis produces a pH drop due to its accumulation in the muscle. The rate of drop may be faster or slower depending on the metabolic status of the muscle. In general, acid pH values (5.6-5.9) may be reached in just a few hours postmortem. Water binding decreases rapidly as pH approaches the isoelectric point of muscle proteins (pi values around 5.0). There is also a tightening of the structure and partial denaturation of myofibrillar proteins. 

Figure 1 Two-dimensional electrophoresis using a tube gel for isoelectric focusing and a slab gel for SDS-PAGE. The proteins are separated in the first dimension on the basis of charge and in the second dimension on the basis of molecular mass. The circles represent proteins, with shading to indicate protein pi values and diameters representing molecular mass. The clotted line shows the direction of separation. (Reproduced with permission from Twyman RM (2004) Principles of Proteomics. Abington, UK Bios/Gatland Publishers.)...

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