Identification and characterization of human ribokinase and comparison of its properties with E. coli ribokinase and human adenosine kinase

Abstract

The catalytic activity of human RK was dependent upon the presence of inorganic phosphate, as observed previously for E. coli RK and mammalian adenosine kinases (AK). A number of activators and inhibitors of human AK, produced very similar effects on the human and E. coli RKs, indicating that the catalytic mechanism of RK is very similar to that of the AKs.

Positron emission tomography probe demonstrates a striking concentration of ribose salvage in the liver

“…To understand ribose salvage in vivo better, we developed a PET probe that mimics the structure of ribose. An earlier study showed that human RBKS can metabolize ribose and, with lower affinity, arabinose (6). This suggested to us that ribose derivatized at the 2-position with a positron-emitting nuclide could be metabolized through the ribose salvage pathway.…”

“…With few exceptions, cells and tissues cannot survive with ribose as their sole carbohydrate source (10)(11)(12). Additionally, RBKS is substrate-inhibited at ribose concentrations of >0.5 mM, suggesting that cells may limit the amount of ribose they salvage (6).…”

“…During salvage, ribose is transported across the cell membrane and phosphorylated by ribokinase (RBKS) to ribose-5-phosphate (6). Ribose-5-phosphate can be incorporated into nucleic acids via the de novo nucleotide synthesis pathway or metabolized to glycolytic intermediates via the nonoxidative pentose phosphate pathway (1).…”

Cloning the Ribokinase of Kinetoplastidae: Leishmania Major

“…The ribokinase gene has been identified from variety of sources including human, E. Coli and Leishmania. There is a high degree of similarity between the ribokinase gene from animal (human) and that from E. Coli (Park et al, 2007). The structure of ribokinase as revealed by X-ray crystal structure of E.coli shows that it is a homodimer in solution with each subunit composed of two domains (Sigrell et al, 1997, Sigrell et al, 1998, Bork et al, 1993.…”

“…Also the crystallographic studies show that oxygen atoms of the α-D-pentofuranose ring are involved in hydrogen bonding interactions between the enzyme and the substrates, ribose and ADP (Andersson & Mowbray 2002, Maj & Gupta 2001. The amino acids residues, asparagines and glutamic acid, at sequence positions 187 and 190, appear to be conserved in all the species studied and have been shown to be the site for phosphate binding (Park et al 2007). Site directed mutation of these amino acid residues have led to formation of mutant enzymes with altered MgATP 2+ and phosphate requirements (Parducci et al, 2006).…”