Simple and complex proteins,

multiprotein complex• A multiprotein complex (or protein complex) is a group of two

or more associated polypeptide chains. If the different polypeptide chains contain different protein domain, the resulting multiprotein complex can have multiple catalytic functions. This is distinct from a multienzyme polypeptide, in which multiple catalyic domains are found in a single polypeptide chain.

• Protein complexes are a form of quaternary structure. Proteins in a protein complex are linked by non-covalent protein-protein interactions and different protein complexes have different degrees of stability over time. Protein complex formation often serves to activate or inhibit one or more of the complex members. In this way protein complex formation can be similar to phosphorylation. A method that is commonly used for identifying the members of protein complexes is immunoprecipitation.

Simple proteins

• Albumin

• Globulin

• Giston

• Prolamin

• Glytelin

• Serum albumin, often referred to simply as albumin, is the most abundant plasma protein in humans and other mammals. Albumin is essential for maintaining the osmotic pressure needed for proper distribution of body fluids between intravascular compartments and body tissues. It also acts as a plasma carrier by non-specifically binding several hydrophobic steroid hormones and as a transport protein for hemin and fatty acids.

• Types• The human version is human serum albumin.• Bovine serum albumin, or BSA, is commonly used in immunodiagnostic

procedures, clinical chemistry reagents, cell culture media, protein chemistry research and molecular biology laboratories (usually to leverage its non-specific protein binding properties).

• Function• Major contributors to oncotic pressure (known also as colloid osmotic

pressure) of plasma; carriers for various substances.• General characteristics• Albumin (when ionized in water at pH 7.4, as found in the body) is

negatively charged. The glomerular basement membrane is also negatively charged in the body; some studies suggest that this prevents the filtration of albumin in the urine. According to this theory, that charge plays a major role in the selective exclusion of albumin from the glomerular filtrate. A defect in this property results in nephrotic syndrome leading to albumin loss in the urine. Nephrotic syndrome patients are sometimes given albumin to replace the lost albumin.

• Because smaller animals (for example rats) function at a lower blood pressure, they need less oncotic pressure to balance this, and thus need less albumin to maintain proper fluid distribution.

• Serum albumin contains eleven distinct binding domains for hydrophobic compounds. One hemin and six long-chain fatty acids can bind to serum albumin at the same time.

• Globulin is one of the two types of serum proteins, the other being albumin. Some globulins are produced in the liver, while others are made by the immune system. The term globulin term encompasses a heterogeneous group of proteins with typical high molecular weight, and both solubility and electrophoretic migration rates lower than for albumin. The normal concentration in blood is 2 to 3.5 g/dl.

• It is sometimes used synonymously with globular protein. However, albumin is also a globular protein, but not a globulin. All other serum globular proteins are globulins.

• Protein electrophoresis is used to categorize globulins into the following four categories:

• Alpha 1 globulins• Alpha 2 globulins• Beta globulins• Gamma globulins (one group of gamma globulins

are immunoglobulins, that function as antibodies)

• Glutelins are soluble in dilute acids or bases, detergents, chaotropic or reducing agents. They are generally prolamin-like proteins in certain grass seeds. glutenin is the most common glutelin as it is found in wheat and is responsible from some of the refined baking properties in bread wheat. The glutelins of barley and rye have also been identified.

• Typically there are HMW and LMW glutelins in these species, they crosslink with themselves and other proteins during baking via disulfide bonds.

• A HMW glutelin (glutenin) of the grass tribe Triticeae can be for coeliac disease in individuals who possess the HLA-DQ8 class II antigen receptor gene. (not yet characterized to the epitope level)

• Prolamins are a group of plant storage proteins having a high proline content and found in the seeds of cereal grains: wheat (gliadin), barley (hordein), rye (secalin), corn (zein) and as a minor protein, avenin in oats. They are characterised by a high glutamine and proline content and are generally soluble only in strong alcohol solutions. Some prolamins, notably gliadin, and similar proteins found in the tribe Triticeae (see Triticeae glutens) may induce coeliac disease in genetically predisposed individuals.