Reaction of 3,4-dihydroxyphenylacetaldehyde (DOPAL) but not dopamine (DA) or 3,4-dihydroxyphenylacetic acid (DOPAC) with glyceraldehyde-3-phosphate dehydrogenase yielded significant protein cross-linking/aggregation. Lane 1, molecular weight marker. Lane 2, control protein. Lane 3, protein with DA. Lane 4, protein with DOPAL. Lane 5, protein with DOPAC. The SDS-PAGE gel was stained with Coomassie. Solid arrows point to the protein monomer (~38 kD) and the open arrow denotes protein aggregates (>200 kD). Note the disappearance of protein monomer in Lane 4 (DOPAL treatment) that correlates with protein aggregation.