hemoglobin

The ancient Greeks knew blood was somehow vital to life, but not until the 19th century could scientists isolate what made it red. In 1851, German-Bohemian chemist Otto Funke, working in Leipzig, managed to crystallize a substance from red blood cells. He called it haemoglobin—from Greek haima (blood) and Latin globus (ball or globe). What Funke held was the first protein ever crystallized from living tissue.

Funke's crystals were remarkable because proteins were thought to be formless, colloidal substances, not orderly geometric structures. Yet here was evidence that the blood's redness could be reduced to pure substance, to order and shape. Over the next decades, chemists measured hemoglobin's iron content—each molecule contained exactly four iron atoms. The iron, they realized, was the key: it bound oxygen reversibly, gripping it in the lungs and releasing it in tissues.

In 1913, Alfred Hempel gave hemoglobin its modern name, standardizing it across languages. By the 1930s, scientists understood that hemoglobin's four iron-containing subunits cooperated—when one grabbed oxygen, it changed shape to help the others bind more readily. This cooperative binding, called allosteric regulation, made hemoglobin far more efficient than a simple iron sponge. The protein was a machine, exquisitely designed.

When Max Perutz and his colleagues mapped hemoglobin's three-dimensional structure in the 1950s—a breakthrough that earned him the Nobel Prize—they saw the four subunits rotating in concert, the iron atoms perfectly placed. The molecule that Funke crystallized a century before emerged as one of nature's masterpieces. Hemoglobin remains the exemplar of how structure determines function in biology.