( ( Since ( ( ( the pH-optimum ) ( of ( ( 4 to ) 6 ) ) ) ( ( can not ) ( be ( achieved ( by ( adding ( ( a catalyst ) ( due ( to ( associated toxicity ) ) ) ) ) ) ) ) ) ) ) ( , ( ( the reaction ) ( ( is ( slow ( in ( live cells ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN Since) (S (NP (NP (DT the) (NN pH-optimum)) (PP (IN of) (NP (QP (CD 4) (TO to) (CD 6))))) (VP (MD can) (RB not) (VP (VB be) (VP (VBN achieved) (PP (IN by) (S (VP (VBG adding) (S (NP (DT a) (NN catalyst)) (ADJP (JJ due) (PP (TO to) (NP (VBN associated) (NN toxicity))))))))))))) (, ,) (NP (DT the) (NN reaction)) (VP (VBZ is) (ADJP (JJ slow) (PP (IN in) (NP (JJ live) (NNS cells))))) (. .)))
Since the pH-optimum of 4 to 6 cannot be achieved by adding a catalyst due to associated toxicity, the reaction is slow in live cells.
(ROOT (S (SBAR (IN If) (S (NP (DT a) (NN catalyst)) (VP (VBZ runs) (PRT (RP out))))) (, ,) (NP (DT the) (NN reaction)) (VP (VBZ slows)) (. .)))