Bodily catalyst (6)
I believe the answer is:
enzyme
'bodily catalyst' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for enzyme that I've seen before include "Catalyst made of protein" , "E.g. pepsin" , "Catalytic protein substance" , "It acts as a catalyst to bring about biochemical reaction" , "Substance produced by living cells" .)