Quantum mechanics

Crystal structure

Biochemistry

Molecule

Physics

Electron density

Organic chemistry

Tetragonal crystal system

Crystallography

Chemistry

Electron

Lysozyme

Proceedings of the Royal Society of London. Series B, Biological sciences

Crystals of hen egg-white lysozyme, grown at pH 4.7 (Alderton &amp; Fevold 1946), are tetragonal with a = b = 79.1 Å, c = 37.9 Å, space group P 4 3 2 1 2 (Palmer, Ballantyre &amp; Galvin 1948; Blake, Fenn, North, Phillips &amp; Poljak 1962). Each of the eight asymmetric units in the cell comprises a single lysozyme molecule, molecular weight about 14 600, together with 1 M sodium chloride solution which constitutes some 33.5% of the weight of the crystal (Steinrauf 1959). The structure of these crystals has been determined by X-ray analysis by the method of multiple isomorphous replacement developed in the studies of haemoglobin (Green, Ingram &amp; Perutz 1954; Blow 1958; Perutz, Rossmann, Cullis, Muirhead, Will &amp; North 1960) and myoglobin (Kendrew, Dickerson, Strandberg, Hart, Davies, Phillips &amp; Shore 1960). Anomalous scattering data were used in conjunction with the isomorphous replacement intensity differences (North 1965) to form a joint probability distribution for the phase of each reflexion. The position of the centroid of each probability distribution gave a phase angle and weighting factor for each reflexion from which the electron density map with minimum r.m.s. error was calculated (Blow &amp; Crick 1959). A large number of different heavy atom derivatives were studied (Poljak 1963; Blake, Koenig, Mair, North, Phillips &amp; Sarma 1965) and three proved satisfactory for calculating an electron density map at 2 Å resolution. They contained respectively ortho -mercuri hydroxytoluene para -sulphonic acid, UO 2 F 5 3- and an ion derived from UO 2 (NO 3 ) 2 , probably UO 2 (OH) n (n-2)-

On the conformation of the hen egg-white lysozyme molecule