Gongorismo derives from a more general base, culteranismo, a Latinizing movement that had been an element in Spanish poetry since the 15th century.
They are believed to act as a general base and general acid.
Naturally occurring SAC uses GTP as a general base in the GTPase reaction catalyzed by G proteins.
Typically, a histidine residue acting as a general base deprotonates the catalytic serine residue and the hydrolytic water molecule.
Substitution of the general base His295 by Ala displays impaired cleavage activity only (H295A retains approximately 1% of wt activity), suggesting that an alternative weaker general base exists in the catalytic site when the general base His295 is mutated.
As described in the "Methods", attempts to find a low-energy reaction path with Tyr351 as the general base failed.
The general base, E254, in all monomers can be modelled in two alternative conformations according to the electron density.
It is somewhat unexpected that substitution of the general base His295 by Ala did not completely eliminate the cleavage activity (Fig. 3); H295A still retains approximately 1% of wt activity, suggesting that an alternative weaker general base exists in the catalytic site when the general base His295 is absent.
From biochemical and structural studies of colicin E9, His103 acts as the general base to deprotonate a water molecule for the hydrolysis of the scissile phosphodiester bond.
In addition, positively charged aa substitution by Lys in H295K did not rescue the catalytic activity, indicating Lys cannot replace His as the general base in HpyAV.
The different metal ion preference of different HNH endonuclease is an interesting phenomenon, given their highly similar set of metal coordinators and general base.
