It is 6 years since we received the tragic news that our great mentor Dr Yasutomi Nishizuka passed away suddenly at the age of 72 years. Dr Nishizuka made several epoch-making discoveries in his life, e.g. the tryptophan metabolism, protein synthesis, ADP-ribosylation, regulation of cAMP-dependent protein kinase and discovery of protein kinase C (PKC). Among them his name will be remembered for a long time as a father of PKC, momentous discoveries in the twentieth century, which are still actively pursued by many laboratories worldwide.