126860-95-5Relevant academic research and scientific papers
STRUCTURE OF ENZYME-BOUND SUBSTRATES: RESONANCE RAMAN AND KINETIC EVIDENCE FOR DIFFERENTIAL ENZYME-SUBSTRATE CONTACTS IN N-(PENTAFLUOROBENZOYL)GLYCINE DITHIOACYL AND THIOACYL PAPAIN
Lee, H.,Angus, R. H.,Storer, A. C.,Carey, P. R.
, p. 1 - 14 (1989)
Resonance Raman (RR) spectroscopy is used to probe the structure of the substrate in the substrate-enzyme complex N-(pentafluorobenzoyl)glycine (dithioacyl) papain (C6F5C(=O)NHCH2C(=S)S-papain.This system was chosen since the high electron withdrawing capacity of the C6F5 group markedly affects electron density of the -NH- moiety which, in turn, is known to change catalytic activity.The RR spectrum of the enzyme-substrate complex is interpreted by reference to the model compound N-(pentafluorobenzoyl)glycine ethyl dithioester (C6F5(C=O))NHCH2C(=S)S-C2H5.The RR spectra of this compound in aqueous or organic solvents can be understood in terms of the known conformational states of N-acylglycine dihtioesters.Comparison of model with enzyme-substrate RR spectra shows that the substrate is binding in the active site in a conformer known as conformer B characterized by a small-NHCH2-CS(thiol) torsional angle and close N-to-S (thiol) contact.Kinetic rate-structure correlations are developed involving k3, the rate constant for deacylation, and the strength of the N-to-S (thiol) interaction.N-(Pentafluorobenzyl)glycine dithioacyl papain fits the rate-structure correlation whereas the corresponding pentafluorobenzoyl glycine thiol intermediate does not.It is proposed that the difference in the size of the C=S compared to the C=O group brings about a small change in the dithioacyl papin compared to the thioacyl papain conformation such that enzyme-substrate contacts involving ortho and meta F atoms in the thiol acyl enzyme case are weakened or removed in the case of the dithioacyl papain.
