Science crossword

[foxygirl]

I am looking for a couple of answers for a science crossword and help would be appreciated.
The regulation of a metabolic pathway by the availability of the products of that pathway. 8 letter word and the 5th letter is B.

An organic molecule that activates an enzyme. 9 letters and the last letter is S
Thanks

[LazyGun]

Feedback regulation of a metabolic pathway.

An organic molecule that activates an enzyme - coenzymes?

[foxygirl]

Thanks LazyGun