Figure 3. The percent distribution of phosphorylated sites in normal human lens proteins identified by using gel-free IMAC phosphopeptide enrichment and LC-MS/MS analysis. A: Proportions of three different phosphorylated amino-acid residues (Ser/Thr/Tyr) in normal human lens extract. Phosphorylation on serine (72%) was more common than threonine (24%) and tyrosine (4%). B: Proportions of the identified proteins with phosphorylation in normal human lens proteins. The proportions of phosphopeptides identified in βB1-crystallin, βB2-crystallin, αB-crystallin, γD-crystallin, filensin, αA-crystallin, and β-crystallin S (or denoted as βs-crystallin) were 12%, 12%, 9%, 8%, 8%, 6%, and 6%, respectively.