Why ATP synthase EC number is 7(Translocase)?

My textbook says it's a hydrolase but when i checked its EC number it was changed to 7.

And also ATPase(adensointriphosphatase) page that was previously classified as hydrolase is deleted in qmul.ac.uk


1 Answer 1


What textbook is this? An ATP synthase is not a hydrolase, since it does not use water to break a chemical bond (at least not in its primary function). However, it couples proton translocation with ATP synthesis. Therefore it is a translocase.

See the following passage from qmul.ac.uk what category 7 is and why e.g. ATPase is classified as translocase rather than as hydrolase. (It is a hydrolase as well, but it's not its primary function.)

Translocases (EC 7): A new EC Class

Six enzyme classes have been recognized since the first Enzyme classification and nomenclature list was first approved by the International Union of Biochemistry in 1961. These were based on the type of reaction catalysed: Oxidoreductases (EC 1), Transferases (EC 2), Hydrolases (EC 3), Lyases (EC 4), Isomerases (EC 5) and Ligases (EC 6). However, it has become apparent that none of these could describe the important group of enzymes that catalyse the movement of ions or molecules across membranes or their separation within membranes. Several of these involve the hydrolysis of ATP and had been previously classified as ATPases (EC 3.6.3.-), although the hydrolytic reaction is not their primary function.

  • 1
    $\begingroup$ Thanks for your answer.I don't think it's a surprise that some "old" sources use this classification because as mentioned in qmul,ATP synthase was classified as 3.6.3 from 2000-2018.And if you don't mind i have another question:Do all enzymes that seem to belong in two classes regrading the direction that we are looking at,are classified regarding the "primary direction" that enzyme usually catalyzes? $\endgroup$
    – PeterA
    Jan 31, 2021 at 17:10
  • $\begingroup$ Unfortunately, it's not that easy. There is a whole catalogue of rules for the naming and classifications of enzymes: qmul.ac.uk/sbcs/iubmb/enzyme/rules.html. $\endgroup$
    – pascal
    Jan 31, 2021 at 17:44

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