Isolated polypeptides or polypeptide chains are modified by di-tyrosine cross-linking such that they retain at least one functional activity. In one embodiment, the isolated polypeptide or polypeptide chains comprise at least one di-tyrosine cross-link, wherein at least one tyrosine of the di-tyrosine cross-link originates from a point mutation to tyrosine, and wherein the di-tyrosine cross-linked protein retains at least one function displayed by the protein in the absence of di-tyrosine cross-linking. In another embodiment, the di-tyrosine cross-linked polypeptide or polypeptide chain has enhanced stability compared to the same polypeptide or polypeptide chain in the absence of di-tyrosine cross-linking. A method for stabilization of a polypeptide or polypeptide complex, by the introduction of intra-polypeptide and/or inter-polypeptide di-tyrosine bonds, which simultaneously maintains the structure and function of the polypeptide or polypeptide complex is also described.