Wednesday, April 13, 2016

Basic Science #7: Albumin

Albumin is a large abundant protein in our blood.  When blood is collected in a tube and left to stand, the red cells, containing hemoglobin will sink to the bottom.  The liquid on top is called serum or plasma.   Albumin gives it the yellowish color.  Serum also contains various components important for our overall health.  The white blood cells and platelets will be in between these two layers - in the interphase.




We should all know about a blood test for Albumin (by my health care provider):
Normal amounts of Albumin: 3.3 - 4.8 g/dL. Albumin is a protein that is made in the liver and released into the blood. It helps keep the blood from leaking out of blood vessels. Albumin also helps carry some medicines and other substances through the blood and is important for tissue growth and healing.
Chemistry of albumin: Human serum albumin - HSA is made of 609 amino acids.  (Yes six hundred and nine amino acids!)  Bovine serum albumin - BSA has a very similar chemistry with small differences in amino acid sequence.   Here is the 3D structure of both proteins pointing out this specific difference:

Human and Bovine Serum Albumin:



The similar structure of albumin in various organisms can be followed from lower organisms to higher ones.  This is the scientific base of evolution.  In comparative genetics the scientists can compare the amino acid sequence of mouse, rat, dog, bovine and human and show the homology.  There is a higher fit or homology between human and bovine, than between human and mouse.
Albumins belong to a group of proteins described as globular proteins, referring to their spherical shape.  This shape makes them soluble in water, so their location in the cell is in the aqueous, or water environment.  Some proteins are membrane proteins which means they are not soluble in water and will be attached to the cell wall or membrane. 
An important aspect of biochemistry of proteins is transport of nutrients or drugs depending on their solubility in water.  Albumin has an important role as a “universal” solvent.  Here you can see how Albumin can attach various molecules as fatty acids which are lipids, or calcium which is a small ion, and transfer them through the blood to their destination in the body.


Albumin attached to various drugs and nutrients:


In this post on Albumin I have introduced the principles of soluble and membrane proteins and some basis of evolution. I hope more people would study these topics and learn to appreciate our amazing complex biology.