No abstract available

[en] Film or area electronic counters are the obvious detection systems for the measurement of X-ray diffraction data from large macromolecules. The single counter of an automatic diffractometer can be used successfully and perhaps to advantage in special cases in which crystal supply is abundant or the irradiated lifetime is long. The decision to use single-counter diffractometry for a particular case depends on the available alternatives and the amount of data and accuracy required to determine the structure. This chapter addresses some of the points that should be considered for diffractometer setup and some procedures for successful data collection. Other details will be found elsewhere in this volume and in cited literature. Specific procedures from our data measurements on the enzyme glycogen phosphorylase a are given. The crystals are P4/sub 3/2/sub 1/2, a = 128.3, c = 116.5. The asymmetric unit has a single polypeptide chain of 97,400 daltons. There are 55,000 unique reflections in the 2.1 A data set