[Study of hydrogen bonds in the "catalytic triad" of trypsin by NMR spectra at 1H, 13C, and 15N nuclei].
The 1H and 13C NMR of trypsin stabilized by chemical modification with a hydrophilic polymer have been obtained in a wide range of pH (1.0-11.0). The spectral features referred to some nuclei of the "catalytic triad" have been identified using different NMR techniques as well as chemical modification with selective reagents. It was found that the monoprotonation of this system results in a quasi-symmetrical hydrogen bond formed between the basic groups which provided explanation for the discrepancies between the experimental findings obtained by different authors concerning the protonation site in this catalytic system. Simulation of the catalytic triad by a 15N-labelled low molecular model suggests that an increase in the OH-group acidity is unaccompanied by a discrete double proton transfer; however, a smooth shift of the bridging protons from one basic atom to another occurs with quasi-symmetrical hydrogen bonds formed in intermediate cases. On the basis of experimental data a new concept has been proposed for the mechanism of acid-base catalysis performed by pains of weak basic groups, such as His-Im and Asp(Glu)-COO- (pKa = 3-7) which are not capable of proton abstraction from alcoholic or water OH-groups (pKa > 13). The catalysis may consist in changing the charge densities on the reacting groups due to strong H-bonding and, on the other hand, in facilitating the free movement of a proton in the field of several basic atoms when going along the reaction coordinate. The energy of very strong hydrogen bonds thus formed diminishes the activation energy of the reaction.
Golubeb
N S
NS
Gindin
V A
VA
Ligaĭ
S S
SS
Smirnov
S N
SN
D002247:Carbon Isotopes; D002384:Catalysis; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D009587:Nitrogen Isotopes; D011522:Protons; D014357:Trypsin / Q000737:chemistry*
D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D011522:Protons; D014357:Trypsin
Issledovanie vodorodnykh sviazeĭ v "kataliticheskoĭ triade" tripsina po spektram IaMR na iadrakh 1H, 13C, i 15N.