Protein amyloid fibrils can be functionalized by coating the core protofilament with high concentrations of proteins and enzymes. This can be done elegantly by appending a functional domain to an amyloidogenic protein monomer, then assembling the monomers into a fibril. To display an array of biologically functional porphyrins on the surface of protein fibrils, we have fused the sequence of the small, soluble cytochrome b562 to an SH3 dimer sequence that can form classical amyloid fibrils rapidly under well-defined conditions. The resulting fusion protein also forms amyloid fibrils and, in addition, binds metalloporphyrins, at half of the porphyrin binding sites as shown by UV-vis and NMR spectroscopies. Once metalloporphyrins are bound to the fibrils, the resulting holo-cytochrome domains are spectroscopically identical to the wild type cytochrome. The concentration of metalloporphyrins on a saturated fibril is estimated to be of the order of approximately 20 mM, suggesting that they could be interesting systems for applications in nanotechnology.