Hemoglobin, a well-known oxygen transport protein in the blood.It plays a role in delivering oxygen received in the lungs to cells throughout the body, but in fact, it was not known where and how gas molecules such as oxygen enter and leave the inside of hemoglobin.

　In this study, a hemoglobin crystal bound with carbon monoxide (CO), which has the same properties as oxygen, is prepared, irradiated with pulsed laser light, and the movement of photodissociated CO is observed by an X-ray crystal analysis method at low temperature. Directly observed.Hemoglobin consists of two α subunits and two β subunits, and one iron in each subunit desorbs oxygen. As a result of observation, the α subunit and β subunit are used. It was found that the movement sites were significantly different, and the route through which CO passed was also different.

　In addition, it is known that hemoglobin changes into a subunit arrangement (R state) where gas easily adheres and a subunit arrangement (T state) where gas does not easily attach, depending on the environment. It was also confirmed that the gas molecules were actively released to the outside of the subunit by exercise.This is said to have been observed even at low temperatures, where the ingress and egress of gas molecules inside and outside the protein is thought to be frozen, and hemoglobin, which has changed to the T state in peripheral tissues with low oxygen concentration, excretes oxygen more quickly. It was suggested that it is a mechanism for supplying to.

　This discovery is expected to lead to the elucidation of the mechanism by which hemoglobin transfers oxygen.

Paper information:[Proceedings of the National Academy of Sciences of the United States of America (PNAS)] Direct observation of ligand migration within human hemoglobin at work