Task: Question Answering
Input (English): Question: In general, allosteric enzymes: 
 Options:  <1> They link the effectors in the active center. <2> They form covalent bonds with their negative effectors. <3> They originate hyperbolic curves of speed before the concentration of substrate. <4> They change their conformation when they link effectors. <5> They are irreversibly modified when they are inhibited.
Output (English): 4