This enzyme is involved in ubiquinone biosynthesis. Ubiquinones from different organisms have a different number of prenyl units (for example, ubiquinone-6 in Saccharomyces, ubiquinone-9 in rat and ubiquinone-10 in human), and thus the natural substrate for the enzymes from different organisms has a different number of prenyl units. However, the enzyme usually shows a low degree of specificity regarding the number of prenyl units. For example, when the COQ5 gene from Saccharomyces cerevisiae is introduced into Escherichia coli, it complements the respiratory deficiency of an ubiE mutant [3]. The bifunctional enzyme from E. coli also catalyses the methylation of demethylmenaquinol-8 (this activity is classified as EC 2.1.1.163) [1].
