EARLY HISTORY AND GENERAL INTRODUCTION

The first discussions in the literature concerning the applications of SR in protein crystallography were given by Harrison (1973), Wyckoff (1973) and Holmes (1974). The first experimental tests were made on SPEAR by Webb et al (1976, 1977) and reported by Phillips et al (1976, 1977); precession photographs of protein crystals were obtained with a 60-fold reduction in exposure times over a home laboratory X-ray source (in this case a conventional fine focus Cu Kα tube running at 1200W) and test data were collected about the iron K edge for rubredoxin and the copper K edge for azurin. The azurin crystal suffered much less from radiation damage in the intense beam than during a longer equivalent exposure on a conventional source. This was the first indication that radiation damage to a protein crystal was less with a more intense X-ray source (figure 10.1). The anomalous dispersion effects using the Fe K edge enabled phases to be determined for rubredoxin with a mean figure of merit of 0.5 (mean phase error of 60°). The anomalous dispersion effects using the Cu K edge were used to confirm the copper sites in azurin utilising phases determined from conventional source data (Adman, Stenkemp, Sieker and Jensen 1978).