Resonance Raman spectra are reported for a series of systematically deuterated analogues of myoglobin in its deoxy state as well as for its CO and O2 adducts. Specifically, the myoglobin samples studied are those that have been reconstituted with deuterated protoheme analogues. These include the methine deuterated, protoheme-d4; analogue bearing C2H3 groups at the 1, 3, 5, and 8 positions, protoheme-d12; the species bearing C2H3 groups at the 1 and 3 positions only, 1,3-protoheme-d6; and the species bearing C2H3 groups at the 5 and 8 positions only, 5,8-protoheme-d6. While the results are generally consistent with previously reported data for synthetic metalloporphyrin models and previous studies of labeled heme proteins, the high-quality low-frequency RR data reported here reveal several important aspects of these low-frequency modes. Of special interest is the fact that, using the two d6-protoheme analogues, it is shown that certain modes are apparently localized on particular pyrrole rings, while others are localized on different rings; i.e., several of these low-frequency modes are localized on one side of the heme. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004