( ( enzymes ( Protein molecules ) ) ( ( ( that act ) as ) ( ( catalysts ( in ( biochemical reactions ) ) ) . ) ) )
(ROOT (S (NP (NNP enzymes) (NNP Protein) (NNS molecules)) (ADVP (NP (DT that) (NN act)) (RB as)) (VP (VBZ catalysts) (PP (IN in) (NP (JJ biochemical) (NNS reactions)))) (. .)))
enzymes Protein molecules that act as catalysts in biochemical reactions.
(ROOT (S (PP (IN In) (NP (DT a) (JJ biological) (NN reaction))) (, ,) (NP (NNS proteins)) (VP (VBP act) (PP (IN as) (NP (NNS catalysts)))) (. .)))