| Coenzyme-Q (ubiquinone; Q) is widely distributed in living organisms and is a component of the mitochondrial respiratory chain. It was thought that in eukaryotes it is present only in the respiratory chain; however, recent developments have shown that it is distributed in all cell membranes. It undergoes oxidation-reduction in cell membranes of lysosomes, golgi and functions as an antioxidant, either by direct reaction with free radicals or by regeneration of vitamins E and C. Prokaryotes such as Escherichia coli synthesize p-hydroxybenzoate (PHB), the precursor of Q, directly from the shikimate pathway via chorismate. Higher animals including humans lack the shikimate pathway and hence synthesize PHB from the essential amino acid tyrosine. However, the steps involved in the formation of PHB from tyrosine are not known. This study shows that Klebsiella oxytoca, can synthesize PHB from chorismate similar to E.coli as well as from tyrosine similar to eukaryotes. A novel alternate PHB biosynthetic pathway that is derived from tyrosine was proposed and provides supporting evidence. |
