Myoglobin and (Sore) Muscles

I have been doing A LOT of walking.  I was warned that this would be the case and I thought I was mentally and emotionally prepared for that, but my feet and legs are SORE.  This was genuinely something I was looking forward to – I like being able to walk places and the public transportation here has been wonderfully easy to navigate – but it has got me thinking a lot about muscles, which of course makes me think of biochemistry.  Biochemistry is chemistry of biological systems, like you and I. You have a body, it does chemistry, it would not function if parts of the various processes that build up or break down molecules don’t happen, so it is pretty important to understand it. 

In biochemistry, there are 4 major classifications of biomolecules – you will probably recognize them from your knowledge of diet and nutrition if not from science classes: carbohydrates, lipids, proteins, and nucleic acids. Proteins have myriad functions and are made up of amino acids.  I am going to focus this post on a single protein: myoglobin. Just by looking at the name, we get lots of information.  The prefix ‘myo-‘ or even just ‘my-‘ refers to muscles.  Think myocardial infarction (obstruction of blood to the heart muscle – a heart attack).  A fun thing I learned as I was checking my memory on the etymology is that the prefix not only refers to muscle, but it also means ‘mouse’ because it was thought that muscles, specifically the biceps, look a bit like mice.  The ‘-in’ ending usually refers to proteins, though that is not all inclusive (like many things in science, there are many exceptions).  The nice thing about organic chemistry and biochemistry is that the prefixes and endings will give you systematic information about the compounds they are describing.  That leaves the middle bit (see how my brain works?  non-linearly) – the ‘-glob-‘ part, which refers to the fact that it is a globular protein, as opposed to a fibrous protein.  I like these classifications because they are visual and intuitive, but for clarity’s sake, a globular protein is globe-like (spherical, globbish – technical term) and a fibrous protein looks more like fibers (woven strands).  Chemically speaking – globular proteins tend to be hydrophobic (non-polar, water fearing, do not mix with water) and fibrous proteins tend to be hydrophilic (polar, water loving, do mix with water).  So much information from name alone.

Myoglobin and, the more commonly known, hemoglobin were studied by a pair of scientists at the Cavendish Lab at Cambridge in the 1950’s. Myoglobin was studied by John Kendrew (1917-1997) and hemoglobin by Max Perutz (1914-2002). Our understanding of protein structure and the ability to predict not just its shape but how it behaves is relatively new science. If you know one protein, you probably know hemoglobin and that it is in red blood cells. It is a globular transport protein that brings oxygen where it is needed in the body via our circulatory system.  Myoglobin stores oxygen in muscle tissue, specifically, which is important as you are working them by walking 5-10 miles per day (hypothetically). Oxygen (O₂) selectively binds to myoglobin better than hemoglobin (I am oversimplifying for purposes of storytelling), so the oxygen gets stored in the muscles more efficiently than it gets transported to the rest of the body. If you are interested in a little more detail about the science behind this, I recommend this Britannica article.

The structure of myoglobin was discovered by Kendrew in 1957 using a technique called x-ray crystallography.  This is significant not just for an increased understanding of myoglobin, but because he was the first to be able to map the atomic structure of ANY protein. He shared the Nobel prize with Perutz for this in 1962.  If you are interested in more biographical info about him, you can find it at the Nobel Prize website. Understanding the 3-D structure of the protein helped researchers to better understand its function. There is still a lot that we do not fully understand about the biochemistry of muscles. Many of the things that I was taught as a student, such as the role of lactic acid in making muscles feel sore, has been found to not be the full picture. Living organisms are complicated systems and there is much still to understand, but that all comes from being able to model the structures that play roles in the process.

The goal of this, then, is to 1) whine about my sore leg muscles, and 2) share that I saw the initial 3-D models that Kendrew used to conceptualize this protein at the Science Museum here in London. The images here are of the 3-D layers (from the x-ray crystallography images) made as plates and then stacked together to look down on the shape and structure (above) and another of the atoms/functional groups placed on sticks at their relative locations so that the protein can be seen through the forest of pegs (below).  I just think this is so cool. It is like one of those 3-D images you have to cross your eyes and blur your vision to see.  As someone who grew up with Tinker Toys, this appeals to both the scientist and my child-like fascination with building. When you reflect, too, on the technology of the day, it is so impressive what scientists were able to determine from relatively small amounts of data…being able to see the forest through the trees.