The paramagnetically shiftedd proton nuclear magnetic resonance spectra of iron-cobalt hybrid hemoglobins [alpha(Co)2beta(Fe)2 and alpha(Fe)2beta(Co)2], as well as those of deoxy forms of cobalt hemoglobin, iron hemoglobin, and their isolated chains, have been measured at 360 MHz. The proton NMR signals of the deoxy forms of iron and cobalt hemoglobins were individually assigned to each subunit. The NMR spectral characteristics of the alpha subunits in deoxycobalt hemoglobin, as well as those in deoxy-alpha(Co)2beta(Fe)2, were found to be quite different from those of beta(Co)2 subunits or isolated alpha-SH chain. Upon ligation of carbon monoxide to the beta(Fe)2 subunits in alpha(Co)2beta(Fe)2, the spectral properties of deoxy-alpha(Co)2 subunits became similar to those of the deoxy-beta(Co)2 subunits. No significant change in the NMR spectrum of the beta(Co)2 subunits was observed in alpha(Fe)2beta(Co)2 upon ligation of carbon monoxide to the alpha(Fe)2 subunits. These observations show the linkage of the electronic structure of the prosthetic groups with the subunits cooperativity in hemoglobin, as well as the inequivalence of the subunits. This is the first report on the paramagnetically shifte proton NMR spectra of the cobalt-substituted hemoproteins.