Crystal Structure of Horse Myoglobin 



of scattering matter S (see Figure 2c), if rotated through 180° about the 

 axis, and then translated through a distance 6/2 parallel to it, must 

 come into coincidence with an identical piece of scattering matter S'. 



/ : 



/ 



a o c 



Figure 2. Unit cell and morphology of horse myoglobin crystals. 



The above data refer to the crystal as grown in approximately 5M 

 phosphate buffer at pH 6-4, and they will be referred to as lattice A. 

 Crystals of myoglobin, however, like other protein crystals, alter their 

 dimensions when placed in different solutions or when dried, and 

 although the poor quality of the crystals has so far prevented a com- 

 plete exploration of the possible lattices, two others have been en- 

 countered. One, known as lattice B, is found when the crystals are 

 placed in saturated phosphate buffer ; the other, known as the dry 

 lattice, is obtained by taking the crystals out into air. The dimensions 

 of all three lattices are given in Table I. 



Table I 

 Cell Dimensions of Horse Metmyoglobin 



It will be noted that the dimensions do not all shrink at equal rates ; 

 a and b are unchanged between A and B, while fi remains unaltered 

 during the transition from B to Dry. 



Assuming a normal density of about 1-27 for the dry crystals (this 

 could not be directly measured because salt-free crystals were not 



151 



