A series of hemo-protein-derived photocatalysts, prepared by reconstitution of the respective apo-proteins with Co(II)-protoporphyrin IX and chemical modification of the protein with the eosin chromophore, is presented. Apo-myoglobin, Apo-Mb, was reconstituted with Co(II)-protoporphyrin IX and further modified with eosin-isothiocynate (3) to yield the photocatalyst Eo(2-)-Mb-Co(II). The protein is loaded by two eosin chromophore units. Photoexcitation of Eo(2-)-Mb-Co(II) yields the electron transfer species Eo(.-)-Mb-Co(I) formed by direct oxidative quenching of (T)Eo(2-)-Mb-Co(II), k(q) = 5.2 x 10(4) s(-1), and via an indirect path where self-quenching of the eosin-chromophore units yields the intermediate redox products (Eo(.3-) + Eo(.-))-Mb-Co(II) that, in the presence of Na-2-EDTA, generate the Eo(.-)-Mb-Co(I) in a secondary dark electron transfer, k(r) = 330 s(-1). The reconstituted protein Eo(2-)-Mb-Co(II) reveals photocatalytic features and its steady-state illumination in the presence of Na(2)EDTA yields hydrogen evolution, phi = 2 x 10(-4), or photohydrogenation of acetylene to ethylene, phi = 1 x 10(-2). The reconstituted photocatalyst Eo(2-)-Mb-Co(II) reveals enzyme-like behavior. Photohydrogenation of acetylenedicarboxylic acid (6) by Eo(2-)-Mb-Co(II) in the presence of Na(2)EDTA reveals stereospecificity and formation of maleic acid as the hydrogenation product kinetics that follows the Michaelis-Menten model, K-m = 4 mM, V-max = 0.6 mu M . min(-1). Similarly, the alpha- and beta-subunits of hemoglobin, Hb, were reconstituted with Co(II)-protoporphyrin IX to yield alpha-Hb-Co(II) and beta-Hb-Co(II). the beta-Hb-Co(II) was specifically modified at cysteine 93 residue by eosin maleimide (4) to form Eo(2-)-beta-Hb-Co(II). The alpha-Hb-Co(II) was modified at a single, unknown, lysine residue by eosin maleimide (4) to generate Eo(2-)-alpha-Hb-Co(II).