The mechanism of ZIF-8 inhibiting PKM2 was studied. Firstly, the effected of 2-MI and zinc acetate on the PKM2 enzyme reaction were investigated. As shown in
Fig. 3A, the activity of PKM2 was not inhibited when high concentrations of 2-MI (100 or 200 μg/mL) were added, but increased. This may be due to the hydrophobic property of 2-MI, which was beneficial to the unfolding of the PKM2 enzyme molecular. Therefore, 2-MI had no inhibitory effect on PKM2. After adding zinc ions (zinc acetate), PKM2 showed a significant inhibition (
Fig. 3B). With the increase of zinc ion concentration, PKM2 activity continued to decrease. Therefore, zinc ions can inhibit PKM2. This is consistent with previous literature [
20]. The IC
50 of zinc ion on PKM2 was about 150 μg/mL, which was much higher than that of ZIF-8. This may be due to the confinement effect of MOFs. Previous studies have reported that the inhibition of PKM2 by zinc ion is mainly due to the interaction between zinc ion and ADP [
20]. The ZnADP complex can be used as competitive or non-competitive enzyme inhibitors. MOFs are organic-inorganic hybrid materials with intramolecular pores formed by self-assembly of organic ligands and metal ions through coordination bonds. It has a large specific surface area and can adsorb various materials from small molecules to large proteins [
29,
30]. ADP could be retained in the pores of ZIF-8, which made it easier to form complexes with zinc ions, thus inhibiting the activity of PKM2 (
Fig. 3C). The results also showed that U-ZIF-8 had stronger inhibitory effect on PKM2 than S-ZIF-8. Different from the usual assumption, it was not because the U-ZIF-8 has larger specific surface area than S-ZIF-8 due to their smaller size. In fact, the specific surface area of U-ZIF-8 and S-ZIF-8 were 1405 and 1446 m
2/g, respectively. The specific surface area of both ZIF-8 was similar because ZIF-8 was porous. The difference of PKM2 inhibition ability of ZIF-8 may be due to the longer pores. When ADP entered the larger size S-ZIF-8, it would affect the subsequent ADP to continue to compound with zinc ions. So, the effective zinc ions compounded with ADP in S-ZIF-8 was less than that in U-ZIF-8 with same weight. The IC
50 of U-ZIF-8 was less than that of S-ZIF-8, and it has better inhibition ability. Therefore, ZIF-8 has a high ability to inhibit PKM2 due to its special structure. The IC
50 was decreased by 1–2 orders of magnitude compared with that of zinc ion.