Lys353 and vanadate plays a significant role. Using QM Region II, we find that the other amino hydrogen of Lys353 is strong hydrogen bonded to the carbonyl of Pro398 (i.e., ρ(O58-H33)=0.033 on average). There are also two significant dihydrogen bonds involving Arg490, namely between H43 and H44 and between H35 and H45; these dihydrogen bonds should restrict the conformation of Arg490. Furthermore, with QM Region II, Pro396 has two hydrogen bonds to Arg360 (ρ(O60-H50)=0.013 and ρ(O60-H66)=0.026 on average); thus, the conformation of Arg360 is also constrained.