1) Myoglobin - 1st model

Myoglobin shown with its backbone as a pink ribbon and with its the proximal and distal histidines shown as ball-and-stick (cyan = carbon, oxygen = red, nitrogen = blue). The heme group is also shown in ball-and-stick, with the iron ion (Fe2+) shown in the center of the heme as a pink sphere.

From Protein Data Bank coordinates 1A6M