Complex sentence: SAM is then converted to 1-aminocyclopropane-1-carboxylic-acid (ACC) by the enzyme ACC synthase (ACS); the activity of ACS determines the rate of ethylene production, therefore regulation of this enzyme is key for the ethylene biosynthesis.
Split into simpler sentences: SAM is then converted to 1-aminocyclopropane-1-carboxylic-acid (ACC) by the enzyme ACC synthase (ACS). The activity of ACS determines the rate of ethylene production, therefore regulation of this enzyme is key for the ethylene biosynthesis.