REFINEMENT OF THE 3-DIMENSIONAL STRUCTURES OF CYTOCHROME C(3), FROM DESULFOVIBRIO-VULGARIS HILDENBOROUGH AT 1.67 ANGSTROM RESOLUTION AND FROM DESULFOVIBRIO-DESULFURICANS ATCC-27774 AT 1.6 ANGSTROM RESOLUTION

The three-dimensional X-ray structures of cytochrome c(3) from Desulfo vibrio vulgaris Hildenborough and from Desulfovibrio desulfuricans ATC C 27774 were previously determined at 1.9 and 1.75 Angstrom resolution , respectively. More recently, higher resolution data were collected ( at 1.67 and 1.6 Angstrom respectively) using synchrotron radiation, Th e refinement of the previously determined three-dimensional structures using the new data resulted in more accurate structural models, with no significant changes of the initial structures. In cytochrome c(3) f rom D. vulgaris Hildenborough, the R-factor was lowered from 19.6 to 1 5.3% using SHELXL-93, complemented with inspection and correction of t he model relative to the electron density. This cytochrome crystallise s in space group P6(1) with a=77.3, b=77.3, c=77.1 Angstrom, Z=12. Cyt ochrome c(3) from D. desulfuricans ATCC 27774 crystallises in space gr oup P6(1)22 with a=62.71, b=62.71, c=111.09 Angstrom, Z=12. The R-fact or was lowered from 17.8 to 16.6% using the same refinement procedure, In this cytochrome the 71-74 loop region was rearranged with no evide nce of the previously found disorder, and disorder models were introdu ced in the terminal regions of residues serine 84 and lysine 90. The r esulting higher-resolution structural models for both cytochromes are analyzed and compared with those previously obtained. (C) 1998 Elsevie r Science S.A. All rights reserved.