The most common and most likely answer to this crossword clue is the 7 letter word ENZYMES
I've seen this crossword clue in Independent
E
N
Z
Y
M
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Buddy explains!

The straight part
We know that "biological catalysts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case biological catalysts = enzymes.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ENZYMES mean?
ENZYMES noun- A globular protein that catalyses a biological chemical reaction.
- Leavened bread, as opposed to azyme