Abstract
Glucose and related hexoses are very important metabolic substrates. Their most important function is to provide quick fuel for most organisms in all three kingdoms because they are the first substrate for energy production in the form of ATP through glycolysis and the subsequent metabolic pathways. In this paper we review the current information about how glucose and related hexoses are transported across biological membranes to carry out their function either as a metabolic molecule or as energy store in marine invertebrate organisms. In these animals, there are two sugar transport systems that are mediated by the sodium/solute symporter family proteins (SGLT) and the major facilitative super-family proteins (GLUT). The most studied sugar transporters in marine invertebrates are involved with dietary sugar uptake, such as SGLT1, SGLT4, GLUT2 and GLUT5, however more studies need to be done to extend the knowledge about these and other sugar transporters involved in metabolic processes.
Highlights
Glucose is the major product of carbon fixation by photosynthetic organisms and it is the most abundant molecule on earth
The most studied sugar transporters in marine invertebrates are involved with dietary sugar uptake, such as SGLT1, SGLT4, GLUT2 and GLUT5, more studies need to be done to extend the knowledge about these and other sugar transporters involved in metabolic processes
The Na+-dependent glucose cotransporters form a family of proteins named SGLT which are coded by the genes SLC5A (Wright, 2001), whereas the Na+-independent glucose transporters are clustered in the family of proteins named GLUT and the corresponding genes are known as SLC2A (Joost and Thorens, 2001)
Summary
Glucose is the major product of carbon fixation by photosynthetic organisms and it is the most abundant molecule on earth. Due to the hydrophilic nature, these processes involve the transfer of glucose (and other hexoses) across the biological lipid bi-layer plasma cell membranes (Wilson-O'Brien et al 2010) This transport is mediated by integral transporter proteins which are classified based on phylogenetic and functional data (Wilson-O'Brien et al 2010). The hexose transporters belong to one of two protein super families: the sodium/solute symporter family (SSSF; (Reizer et al 1994)) and the major facilitative super-family (MFS; (Marger and Saier Jr, 1993; Pao et al 1998; Saier Jr, 2000)) whose Pfam numbers in the database http://pfam.janelia.org are PF00474 and CL0015 respectively Both sodium dependent and facilitated transport have been widely studied in humans and other mammals (Zhao and Keating, 2007; Aschenbach Jr et al 2009). Little is known about sugar transport in invertebrate animals and even less in marine invertebrates; in this review we compiled the information to provide an overview and understand glucose and related hexoses uptake and importance
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