Table 1.

Specific activities of 50S subunits and KSP particles

Ribosomal particles*	Peptidyl transferase activity, cpm†
50S subunits	8,780  ±  120
KSP15	210  ±  40
KSP30	200  ±  40
KSP50	3,910  ±  890
KSP80	3,620  ±  700
No ribosomes	260‡  ±  40

^*50S subunits or KSP particles (0.2 A₂₆₀) were used in the peptidyl transferase assay. KSP particles were prepared by treatment of 50S subunits with proteinase K, SDS, and one phenol extraction, separated by sucrose gradient centrifugation, and precipitated from the gradient peaks (see Fig. 1B) by 3 volumes of ethanol. 

^†Average of two independent experiments. 

^‡The background ethyl acetate-extractable radioactivity apparently corresponds to unidentified methanolysis products of fMet-tRNA (50).