Most biochemical reactions are attended by the consumption or liberation of protons, a fact that necessitates the inclusion of a pH buffer in most enzyme rate measurements. For maximal buffer capacity, the buffer's pKa should be roughly the same as the desired experimental pH, thus bringing about a minimal change in sample pH. Ideally, the buffer's pK does not change much with changes in temperature, and only controls the hydrogen ion concentration. Moreover, while investigators often fastidiously verify the chemical purity of enzyme and substrates used in a study, they often ignore the possibility that commercial buffer salts are contaminated with metal ions and other chemically reactive species. Workers should not overlook the likely possibility that the enzyme may bind a species of the buffer that alters the kinetic properties of the enzymatic site. Alberty (2006) reminds us that when the pH of a buffer is changed, the [Bufferx-]/[H • Buffer(x-1)-] ratio (e.g., for phosphate buffer, the researcher might work in the range where
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