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, which is why animals that can hold their breath for long periods, like whales and seals, have a lot of myoglobin in their muscles. This protein is made of certain building blocks called amino acids and contains iron, which allows it to bind to oxygen.

Myoglobin is different from hemoglobin, the protein in red blood cells that carries oxygen throughout the body. Myoglobin has a stronger attraction to oxygen than hemoglobin does, which means it can hold onto oxygen more tightly. This helps muscles keep oxygen when it’s 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 important work, they won the Nobel Prize in Chemistry in 1962. Even though myoglobin seems important, scientists have found that mice without it can still live normally. However, these mice change in ways that suggest myoglobin helps bring oxygen to muscles and protect cells from harmful substances.

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 onto oxygen. When meat is cooked well done, it turns brown as the iron inside changes.

Some meats stay pink even after cooking because they have added substances that keep the iron in its red form. This can make the meat look fresher than it is. Companies have made plant-based meats that copy this color using special processes.

Role in disease

When muscle tissue is damaged, myoglobin is released into the bloodstream. High levels of myoglobin can be a sign of muscle damage and might indicate problems like rhabdomyolysis. The kidneys filter myoglobin, but it can harm kidney cells and lead to kidney injury.

Doctors sometimes check myoglobin levels to help find out if someone is having a heart attack, especially if they have chest pain. However, myoglobin alone isn't always enough to confirm a heart attack, so doctors also look at other tests and symptoms.

Structure and bonding

Myoglobin is part of a group of proteins called globins and, like these proteins, it has eight special spiral shapes called alpha helices connected by loops. In humans, myoglobin has 154 tiny building blocks called amino acids.

Myoglobin has a special ring-shaped part called a porphyrin, with a metal called iron in the middle. A group called histidine attaches directly to the iron, and another histidine group is nearby, ready to help hold onto oxygen. This helps myoglobin bind to oxygen but not as strongly to a gas called carbon monoxide. When oxygen binds to the iron, the iron changes shape slightly and moves into the center of a pocket, allowing myoglobin to carry oxygen effectively.

Synthetic analogues

Scientists have made many models of myoglobin to study how it works. One famous example 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 bind to oxygen gas (O₂). The oxygen takes a bent shape and attaches to the iron.

One important feature of this model is that it slowly forms an inactive state called the μ-oxo dimer. In real myoglobin inside living things, the protein structure stops this from happening, keeping the iron working properly.