An enzyme catalyzing the synthesis of a specific substance. Synthetase is limited, in the Enzyme Commission Report, to use as a trivial name for the ligases (EC class 6), which in turn are those synthesizing enzymes that require the cleavage of a pyrophosphate linkage in ATP or a similar compound. Reversal of lyase (EC class 4) reactions, producing a synthesis, is indicated (in trivial names) by synthase; such reactions do not involve pyrophosphate cleavage. For individual synthetases, see the specific names.
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Examples: glitazone, GI cocktail, etc.