Figure 1. Overall structure (A) and topology diagram (B) of A. suum cytochrome b₅.

The protein is folded in six helices and five β strands, comprising a β-pleated sheet. (A) Ribbon and ball-and-stick drawing of the overall structure. The six helices are numbered 1, 2, 3, 4, 4A and 5 in grey, while the five β strands are denoted A–E in dark grey. The haem and His³⁸, His⁶², Cys¹ and Cys⁷⁷ are drawn as ball-and-stick models. (B) α-Helices and β-strands are represented as rectangles and broad arrows respectively, with residue numbers showing their starting and ending positions. Two histidine residues (His³⁸ and His⁶²) ligating the haem iron and the disulphide bond between Cys¹ and Cys⁷⁷ are also shown. The nomenclature of α-helices and β-strands is the same as in (A).