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Two crystal forms of beta-galactosidase have been obtained from Escherichia
coli. One crystal form is hexagonal space group P6222 or enantiomorph, with cell
dimensions a = b = 154 A, c = 750 A. The second form is monoclinic, space group
P21, with cell dimensions a = 107.9 A, b = 207.5 A, c = 509.9 A, beta = 94.7
degrees. The monoclinic form seems better suited to detailed structural
analysis. The crystals are radiation-sensitive, but by using synchrotron
radiation in conjunction with a long (400 mm) crystal-to-film distance it was
possible to resolve the individual reflections. On the basis of crystal density
measurements, there are four tetramers each of molecular weight 465,000 per
asymmetric unit. The Patterson function strongly suggests that two of the
tetramers are related to the other two by translation. The data are consistent
with the tetramers having 222 point symmetry, but this is not proven.
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