Ketohexokinase (ATP: d-fructose 1-phosphotransferase) initiates fructose breakdown via the modified EMP pathway in halophilic archaebacteria

Ketohexokinase, catalysing the ATP-dependent phosphorylation of d-fructose to fructose 1-phosphate was identified as the enzyme responsible for the initiation of fructose breakdown via the modified EMP pathway in the halophilic arachaebacterium Haloarchla vallismortis. The phosphorylated product was identified as fructose 1-phosphate through its conversion to (i) a biphosphate ester by H. vallismortis 1-phosphofruktokinase, and (ii) trioses by rabbit muscle aldolase. The product of ketohexokinase reaction gave glyceraldehyde and dihydroxyacetone phosphate when cleaved directly by mammalian muscle aldolase, whereas, glyceraldehyde 3-phosphate and dihydroxyacetone phosphate were produced when it was converted to the biphosphate ester prior to the treatment with aldolase. This is a first demonstration of ketohexokinase not only in an arachaebacterium but also in a prokaryote.