Hemoglobin

I stumbled across hemoglobin while I was studying for toxicology. The body's oxygen carrier is a pretty cool molecule. Here are some pictures that I drew in PyMOL during little "studying breaks". They are made from the XRD structure from Protein Data Bank. Thinking about it, it seems pretty cool that we can actually visualise molecular structures and that we get the same results when we model them in a computer.

On this one you can see the whole tetramer. The four heme groups are shown in yellow.

Heme is the center-piece of the molecule (or as they say prosthetic group). The O₂ is right in the middle. Underneath is the Fe²⁺. It's bonded to the oxygen, the 4 nitrogens of the porphyrin ring, and the nitrogen of His⁸⁷ which is the covalent connection to the protein (hence prosthetic group).

A hydrogen of His⁵⁸ is very close to the O₂. Good for it that it is bent away. You could imagine that linear CO wouldn't be quite as comfortable in there. This is probably one of the reasons why the affinity of hemoglobin for CO is much lower than that of isolated heme.

This is heme with its whole subunit. You can see how the two histidines (the covalently bonded one and the steric hindrance) come from different helices.

Doing all this makes me wonder which I like better quantum chemistry or theoretical biochemistry. I'll get to take a glance into both of them this summer hopefully. Maybe I'll know more then.