CHARACTERISTICS OF THE PARAMAGNETIC H-1-NMR SPECTRA OF THE FERRICYTOCHROME C-551 FAMILY

Heme proton resonances have been assigned for ferricytochromes c-551 i solated from four distinct species of bacteria. While the available st ructure information indicates that the four cytochromes have very simi lar conformations in solution, including the chirality of the methioni ne ligand sulfur bond, the chemical shifts of the paramagnetically shi fted resonances are surprisingly different, more so than has been prev iously reported for a homologous series of ferricytochromes. The reson ances are contrasted in terms of chemical shift and the temperature de pendence of the shift, which gives rise to a very strong anti-Curie ef fect for some specific protons. Non-methyl heme resonances do display an approximately conserved set of chemical shifts, but the heme methyl groups demonstrate a wide range of values. The 12(1) heme methyl grou p is always the highest frequency heme methyl, but the relative positi ons of the other methyl groups may change. The 7(1) heme methyl group always displayed strong anti-Curie behavior, while the 12(1) methyl gr oup displayed normal Curie behavior. The behavior of the other methyl groups was variable. Possible reasons for the range of observations wi ll be discussed. In spite of their NMR differences, all the ferricytoc hromes c-551 demonstrated comparable electron-transfer rates to a memb rane-bound cytochrome reductase system.