using stereospecifically labelled ( sp ) - ( rp ) - [ beta-17o ] gtp ( prepared by modification of a previously published procedure which is now also suitable for guanine nucleotides ) , it was found that only one of the two possible diastereomers ( sp ) led to detectable line-broadening of the epr spectrum of mn2+ at the active site of ef-tu ( linewidth 1.5 mt ) , whereas the rp isomer caused the same linewidth as unlabelled nucleotide ( 1.3 mt ) .
C0018353
gtp
C0018328
guanine