Sialic Acid (N-Acetylneuraminic Acid) as the Functional Molecule for Differentiation between Animal and Plant Kingdom

Organisms synthesize saccharides for carbohydrates, amino acids for proteins, fatty acid for lipids and nucleotides for nucleic acids for the basic molecules. Recently, carbohydrates have been recognized as the 3rd life chain molecule in eukaryotic cells. One of the biggest differences between the plant and animal kingdom would be the existence of the 9-carbon monosaccharide, sialic acid or N-acetylneuraminic acids (Neu5Ac) (Figure 1). Even some enterobacterial species produce the sialic acids, although their origins are postulated to be probably derived from the bacteria-host interactions during long evolution. Some sialic acid-like saccharides such as legionaminic acid were also found in bacteria. The interesting point will be then what is the motivation of the acquisition of the 9-carbon sialic acid from the carbohydrate biosynthesis and functional distribution of these animals and bacteria. This fundamental question is linked to the paradoxical question why do not the plants contain the sialic acids? Interestingly, these two organisms of bacterial and animals can move to place to place as the behavioral characters, where the process is indeed called “biological adaptation” or “evolution”. The organism’s movement process needs their consideration, thought, memory, learning and education, as these processes are specialized for the mobile organisms. Actually the contents of sialic acids of human brain is the most highest among those of the current organisms through all the animals, as human is the mostly evolved organism. The more the content of sialic acids is high the more the organism is evolved. Then the sialic acids are thought to be the movement-related molecules. How do the molecules play their roles in cells, tissues, organs, and organisms If the sialic acids are such functional? The prospective answer will be based on the molecular interactions of the sialic acids and their counterparts in each specific cell or site of each organism [1-3]. Biological functionof Sialic Acids