Oxygen binding in the lungs triggers a conformational change through _________ histidine movements.

The correct choice highlights the mechanism by which oxygen binding to hemoglobin results in a conformational change that is crucial for effective oxygen transport. In hemoglobin, the binding of oxygen occurs at the heme group, which contains an iron atom that can interact with oxygen. When oxygen binds to the iron, it pulls the iron atom into the plane of the heme, which subsequently affects the surrounding structure of hemoglobin.

This process involves the movement of histidine residues that are located near the heme group. Specifically, the ‘proximally’ positioned histidine, known as the F8 histidine, is directly bonded to the iron atom of the heme group. When the iron moves upon oxygen binding, the F8 histidine moves as well. This movement is pivotal because it initiates a series of conformational changes throughout the hemoglobin protein structure, allowing for the cooperative binding of additional oxygen molecules.

The other options do not accurately describe the mechanism involved in oxygen binding and subsequent conformational changes in hemoglobin. Thus, the understanding of proximal histidine movement is fundamental in grasping how hemoglobin functions in oxygen transport and release.