Cytosolic pantothenate kinases catalyze the reaction of ATP and pantothenate to form ADP and phosphopantothenate. This enzymatic activity has been demonstrated in crude cell extracts for two isoforms of mouse pantothenate kinase 1 (Rock et al. 2002) and for their human homologues (Ramaswamy and 2004). Two additional human genes, PANK3 and PANK4, encode closely related proteins but pantothenate kinase activity has not been demonstrated experimentally for them (Leonardi et al. 2005; Zhou et al. 2001).