I te tau 1929, ka wehe a Northrop i te pepsin whākōkī o te whākōkī, ā, ka whakatau ko te pūmua tērā.
Ko te tikanga, ko te putanga matatini ake o te rerenga korero ko "I te tau 1929, i wehehia e ia te pepsin enzyme kopu me te whakatau ko te pūmua, a i te 1938 i wehehia e ia me te crystallized te bacteriophage tuatahi (he huaketo iti e whakaeke ana i te huakita), a i whakatau ko te nucleoprotein. "