( ( Before ( ( the discovery ) ( of ribozymes ) ) ) ( , ( ( ( ( enzymes , ) ( which ( are ( defined ( as ( catalytic proteins ) ) ) ) ) ) , ) ( ( were ( the ( ( only known ) ( biological catalysts ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN Before) (NP (NP (DT the) (NN discovery)) (PP (IN of) (NP (NNS ribozymes))))) (, ,) (NP (NP (NNS enzymes)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBP are) (VP (VBN defined) (PP (IN as) (NP (JJ catalytic) (NNS proteins))))))) (, ,)) (VP (VBD were) (NP (DT the) (ADJP (RB only) (VBN known)) (JJ biological) (NN catalysts))) (. .)))
Before the discovery of ribozymes, enzymes, which are defined as catalytic proteins, were the only known biological catalysts.
(ROOT (S (NP (NP (DT The) (NN discovery)) (PP (IN of) (NP (NNS ribozymes)))) (VP (VBD nullified) (NP (DT the) (NN idea)) (SBAR (IN that) (S (NP (DT all) (JJ biological) (NNS catalysts)) (VP (VBP are) (NP (NNS proteins)))))) (. .)))