AN UNUSUAL CONFORMATION OF THE METHIONINE HEME LIGAND IN CYTOCHROME-C(L) ESTABLISHED BY 2-DIMENSIONAL H-1-NMR

A complete relaxation-matrix analysis of NOESY cross-peak intensities was used to determine the conformation of the methionine ligand to the haem group in two ferrocytochromes c(L) from Methylophilus methylotrophus and Methylobacterium extorquens, including the configuration at the sulphur. The conformation of the axial methionine is of a type reported only for the cytochromes c, from Pseudomonas mendocina and Azorobacter vinelandii. Although the conformation of the methionine is unusual, the paramagnetic shifts of the haem methyl proton resonances in the oxidized proteins indicate that the electronic structure of the haem groups is similar to that found in the mitochondrial type of cytochrome c.