The adhesive and cohesive properties of the amino acid L-3,4-dihydroxyphenylalanine (DOPA) have been widely explored as a potential material for adhesion, based, among other things, on the biological system of blue mussel extracellular byssal threads and foot proteins. Proteins containing DOPA are generated within mammalian cells by oxidation of tyrosine residues during periods of oxidative stress. By generating proteins containing DOPA, in vitro, through the (mis)incorporation of DOPA during protein synthesis, we are able examine the role and fate of DOPA-containing proteins in mammalian cells. We demonstrate a decrease in catabolism of long half-life cell proteins and an increase in cellular autofluorescence when DOPA is present in cell proteins. We provide evidence for the formation of DOPA derivatives which can be detected in proteins after 14C-DOPA incorporation by HPLC analysis. Additionally, we demonstrate that the cells upregulate the expression of genes required to handle damaged proteins and protein aggregates under these conditions. Substantial evidence for DOPA derivatives and cross-linking has previously been shown in extracellular blue mussel byssal threads; here we provide evidence for cell-associated DOPA derivatives in mammalian cells.