Myoglobin

Myoglobin is a special kind of protein found in the muscles of animals, especially in mammals like humans, whales, and seals. It helps muscles store oxygen. This is why animals that can hold their breath for long periods, like whales and seals, have a lot of myoglobin in their muscles. Myoglobin is made of building blocks called amino acids and contains iron, which lets it hold onto oxygen.

Myoglobin is different from hemoglobin, the protein in red blood cells that carries oxygen around the body. Myoglobin holds onto oxygen more tightly than hemoglobin does. This helps muscles keep oxygen when it is not being used right away.

In 1958, scientists John Kendrew and Max Perutz discovered the exact shape of myoglobin using a special imaging technique called X-ray crystallography. For this work, they won the Nobel Prize in Chemistry in 1962. Scientists have found that mice without myoglobin can still live normally, but they act in ways that show myoglobin helps bring oxygen to muscles.

Differences from hemoglobin

Myoglobin is a special protein in our muscles that helps carry oxygen, just like hemoglobin does in our blood. But there are some key differences. Myoglobin has only one part that holds oxygen, while hemoglobin has four. This means myoglobin can hold onto oxygen more tightly than hemoglobin can. This helps make sure our muscles get the oxygen they need, especially when we are working hard.

Role in cuisine

Myoglobin helps give meat its color. In fresh meat, it makes the meat look red because it holds oxygen. When meat is cooked well done, it turns brown.

Some meats stay pink after cooking because they have added substances. This can make the meat look fresher. Companies have made plant-based meats that copy this color.

Role in disease

When muscle tissue is damaged, myoglobin can enter the bloodstream. High levels of myoglobin may show that muscle damage has occurred and could mean there are problems like rhabdomyolysis. The kidneys filter myoglobin, but it can sometimes affect kidney cells.

Doctors may check myoglobin levels to help see if someone is having a heart attack, especially if they have chest pain. But myoglobin alone does not always prove a heart attack, so doctors also use other tests and look at symptoms.

Structure and bonding

Myoglobin is a type of protein called a globin. It has eight spiral shapes called alpha helices linked by loops. In humans, myoglobin is made of 154 small units called amino acids.

Myoglobin contains a ring-shaped part called a porphyrin with a metal called iron in its center. A group called histidine connects directly to the iron, and another histidine group is close by, helping myoglobin hold onto oxygen. This allows myoglobin to carry oxygen well, but it does not bind as strongly to a gas called carbon monoxide. When oxygen attaches to the iron, the iron shifts slightly, helping myoglobin transport oxygen effectively.

Synthetic analogues

Scientists have made models of myoglobin to learn how it works. One famous model is called the picket fence porphyrin. This model uses a special kind of iron and a bulky chemical called tetraphenylporphyrin. When a substance called imidazole is added, this model can hold onto oxygen gas (O₂). The oxygen takes a bent shape and sticks to the iron.

One important thing about this model is that it slowly changes into an inactive state called the μ-oxo dimer. In real myoglobin inside living things, the protein stops this from happening, so the iron keeps working properly.