Limited proteolysis of myoglobin opens channel in ferrochelatase-globin complex for iron to zinc transmetallation

•Partial pepsin proteolysis of myoglobin enhances formation of zinc protoporphyrin IX.•Recombinant ferrochelatase may find practical use for color formation in meat curing.•Salt protects ferrochelatase against chemical and thermal denaturation.•Zinc/iron transmetallation proceed through a myoglobin-enzyme-zinc tertiary complex.