Authors

Discussion

D-arabinopyranose (D-Arap) is found, uniquely, in cell surface glycoconjugate structures of certain trypanosomatid parasites: Leishmania major lipophosphoglycan, Crithidia fasciculata lipoarabinogalactan and Endotrypanum schaudinni glycoinositol phospholipids. The activated donor molecule of D-Arap has been identified in L. major as GDP-α-D-Arap. So far it is known that both L. major and C. fasciculata have a salvage pathway allowing the parasites to internalize D-Ara from the extracellular medium or the lumen of the insect guts and convert it to GDP-α-D-Arap via an arabinose-1-kinase/pyrophosphorylase. A de novo pathway, whereby D-Glucose is converted to D-Arap via loss of the Glc C-1 carbon atom has been postulated but many details are missing. Many gram-negative bacteria have an Arabinose-5-phosphate isomerase enzyme. In bacteria API enzymes catalyse the interconversion of D-ribulose-5-phosphate, the product of the oxidative phase of the pentose phosphate pathway, and D-arabinose-5-phosphate. We speculate that trypanosomatids may also convert D-Glc to D-Arap via Ru5P and its isomerisation to A5P followed by dephosphorylation to D-Arap. Apart from cell surface incorporation it is possible that D-Arap may be used by all the kinetoplastids to make D-erythroascorbate, similar in structure and physicochemical properties to Vitamin C.