Atypical kinase involved in the biosynthesis of coenzyme Q, also named ubiquinone, an essential lipid-soluble electron transporter for aerobic cellular respiration (PubMed:21296186, PubMed:25498144, PubMed:25540914, PubMed:27499294, PubMed:36302899, PubMed:38425362). Its substrate specificity is still unclear: may act as a protein kinase that mediates phosphorylation of COQ3 (By similarity). According to other reports, acts as a small molecule kinase, possibly a lipid kinase that phosphorylates a prenyl lipid in the ubiquinone biosynthesis pathway, as suggested by its ability to bind coenzyme Q lipid intermediates (PubMed:25498144, PubMed:27499294). However, the small molecule kinase activity was not confirmed by another publication (By similarity). Shows an unusual selectivity for binding ADP over ATP (PubMed:25498144). {ECO:0000250|UniProtKB:Q96D53, ECO:0000269|PubMed:21296186, ECO:0000269|PubMed:25498144, ECO:0000269|PubMed:25540914, ECO:0000269|PubMed:27499294, ECO:0000269|PubMed:36302899, ECO:0000269|PubMed:38425362}. This is the function of COQ8A (coenzyme Q8A, Ensembl gene identifier ENSG00000163050).