Editing Lysozyme (section)

==== Phillips ====
The Phillips mechanism proposed that the enzyme's catalytic power came from both steric strain on the bound substrate and electrostatic stabilization of an [[Oxocarbenium|oxo-carbenium]] intermediate. From X-ray crystallographic data, Phillips proposed the active site of the enzyme, where a hexasaccharide binds. The lysozyme distorts the fourth sugar (in the D or -1 subsite) in the hexasaccharide into a half-chair conformation. In this stressed state, the glycosidic bond is more easily broken.<ref>{{cite journal | vauthors = Blake CC, Johnson LN, Mair GA, North AC, Phillips DC, Sarma VR | title = Crystallographic studies of the activity of hen egg-white lysozyme | journal = Proceedings of the Royal Society of London. Series B, Biological Sciences | volume = 167 | issue = 1009 | pages = 378–388 | date = April 1967 | pmid = 4382801 | doi = 10.1098/rspb.1967.0035 | s2cid = 35094695 | bibcode = 1967RSPSB.167..378B }}</ref> An ionic intermediate containing an [[Oxocarbenium|oxo-carbenium]] is created as a result of the glycosidic bond breaking.<ref name="Application of secondary alpha-deut">{{cite journal | vauthors = Dahlquist FW, Rand-Meir T, Raftery MA | title = Application of secondary α-deuterium kinetic isotope effects to studies of enzyme catalysis. Glycoside hydrolysis by lysozyme and β-glucosidase | journal = Biochemistry | volume = 8 | issue = 10 | pages = 4214–4221 | date = October 1969 | pmid = 5388150 | doi = 10.1021/bi00838a045 }}</ref> Thus distortion causing the substrate molecule to adopt a strained conformation similar to that of the [[transition state]] will lower the energy barrier of the reaction.<ref name="McKenzie_1991">{{cite journal | vauthors = McKenzie HA, White FH | title = Lysozyme and α-lactalbumin: structure, function, and interrelationships | journal = Advances in Protein Chemistry | volume = 41 | pages = 173–315 | year = 1991 | pmid = 2069076 | doi = 10.1016/s0065-3233(08)60198-9 | isbn = 978-0-12-034241-9 }}</ref>

The proposed oxo-carbonium intermediate was speculated to be electrostatically stabilized by aspartate and glutamate residues in the active site by [[Arieh Warshel]] in 1978. The electrostatic stabilization argument was based on comparison to bulk water, the reorientation of water dipoles can cancel out the stabilizing energy of charge interaction. In Warshel's model, the enzyme acts as a super-solvent, which fixes the orientation of ion pairs and provides super-[[solvation]] (very good stabilization of ion pairs), and especially lower the energy when two ions are close to each other.<ref>{{cite journal | vauthors = Warshel A | title = Energetics of enzyme catalysis | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 75 | issue = 11 | pages = 5250–5254 | date = November 1978 | pmid = 281676 | pmc = 392938 | doi = 10.1073/pnas.75.11.5250 | doi-access = free | bibcode = 1978PNAS...75.5250W }}</ref>

The [[rate-determining step]] (RDS) in this mechanism is related to formation of the [[Oxocarbenium|oxo-carbenium]] intermediate. There were some contradictory results to indicate the exact RDS. By tracing the formation of product ([[4-Nitrophenol|p-nitrophenol]]), it was discovered that the RDS can change over different temperatures, which was a reason for those contradictory results. At a higher temperature the RDS is formation of glycosyl enzyme intermediate and at a lower temperature the breakdown of that intermediate.<ref>{{cite journal | vauthors = Weber JP, Fink AL | title = Temperature-dependent change in the rate-limiting step of β-glucosidase catalysis | journal = The Journal of Biological Chemistry | volume = 255 | issue = 19 | pages = 9030–9032 | date = October 1980 | pmid = 6773958 | doi = 10.1016/S0021-9258(19)70521-3 | doi-access = free }}</ref>
[[File:Lysozyme glycosyl covalent intermediate.gif|thumb|Covalent intermediate of lysozyme enzyme, with covalent bond in black and experimental evidence as blue mesh.<ref>{{Cite web|url=http://proteopedia.org/wiki/index.php/Lysozyme#Covalent_intermediate_and_product_complex|title = Hen Egg-White (HEW) Lysozyme - Proteopedia, life in 3D}}</ref>]]