We have also reported the results of an AIM study to ascertain the complex hydrogen bonding in VCPO. Many hydrogen bonds which are not apparent by consideration of distances became apparent. It is particularly notable that the conformations of Lys353, Arg360 and Arg490 are restricted because of various hydrogen bonds, and this restriction of conformations may enhance the rate of catalysis. Table . With QM Region II, the following bond lengths (in Å) and bond angle (O4-V-N5) were calculated for optimized structures where 1-23 are the input structures. n/a means "not applicable": one or both of the atoms were not present. "NC" means ρ value was not calculated, and it is expected to be greater than 0.1. A value of ρ=0 indicates that there is no density between these atoms, and hence there is no bond between these atoms.