Friday, July 15, 2016

Amino acids with acidic side chains

This is the latest group of standard amino group that I will describe. It consists of 2 amino acids, glutamate (also called glutamic acid) and aspartate (also called aspartic acid). Both have a carboxylic group in its side chain, which, being a weak acid group, confers acidic properties to the side chain. In other words, these side chains tend to have a negative charge as a result of deprotonation of the carboxylic group. They are, therefore, very important amino acids to establish ionic interactions with amino acids with alkaline side chains (more information on these amino acids here), and these forces may also be called salt bridges. In order to avoid confusion in the nomenclature of the carboxylic group of the side chain and the carboxylic group attached to the alpha carbon, the side chain group is typically referred to as gamma-carboxylic. The difference between glutamate and aspartate is just a methylene group -CH2 -. Indeed, glutamate has one more carbon (in the form of methylene group) than aspartate. Both can be obtained from intermediates of the Krebs cycle (glutamate from alpha-ketoglutarate and aspartate from oxaloacetate), and besides being building blocks for protein synthesis, they are also used as neurotransmitters. Glutamate also plays a very important role in terms of the sense of taste, and is also important as a donor of amino groups in several reactions of biosynthesis of nitrogenous molecules.

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