Seeing a carbon-monoxide molecule escaping from the clutches of the Myoglobin protein
Myoglobin, also known as the hydrogen atom of protein structures, normally binds and transports oxygen molecules (O) around blood-stream. The actual binding to O is done by a heme group trapped in the heart of the myoglobin structure. One of the remarkable things is that by itself, a heme molecule will prefer to bind to CO rather than O. But when the heme is trapped in myoglobin, the myoglobin structure ejects the CO from the heme if it happens to bind.
This following movie is a direct measurement of the ejection of CO from the heme in a molecule of myoglobin. Incredibly sensitive – the movie occurs in 0.00000316 s of real time – time-resolved X-ray crystallography is used to directly observe changes in the electron density of the CO, the heme and myoglobin: