Crossword Genius

Something added in assayin' enzyme (7)

Ross

I believe the answer is:

trypsin

'enzyme' is the definition.

'something added in assayin'' is the wordplay.
'something added' becomes 'ps' (PS in a letter).
'in' means one lot of letters goes inside another.
'assayin'' becomes 'tryin' ('trying' pronounced like 'assaying' was; 'try' can be a synonym of 'assay').
'ps' put inside 'tryin' is 'TRYPSIN'.

(Another definition for trypsin that I've seen is " substance to help digestion".)

I've seen this clue in The Times.
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