Lysine positive charges

Serine proteases usually show primary specificity (occupation of subsite Si) for positively charged arginine or lysine (trypsin, plasmin, plasminogen activators, thrombin), large hydrophobic side chains of phenylalanine, tyrosine, and tryptophan (chymotrypsin, cathepsin G, chymase, and subtilisin), or small aliphatic side chains (elastases). Nevertheless, there are a large number of variations and in many cases, other subsites like S2 and S3 are more discriminating while maintaining the... 

RNase A is a basic protein with an isoelectric point (pi) of 9.45 and a net positive charge in neutral solution.35 However, the conversion of positively charged lysine side chains to polar, but neutrally charged, methylol adducts would be expected to lower the pi of formalin-treated RNase A. To explore this further, RNase A was treated with 5% formalin and analyzed by isoelectric focusing (IEF) gel electrophoresis. Figure 15.5a shows that the pi values were shifted into the pH 6.0-7.4 range. Figure 15.5b shows the results of IEF... 

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