The effects of sulfhydryl-blocking reagents on canine pancreatic ribosomes

Abstract

Incubation of canine pancreatic ribosomes with 1 m m-PHMB 1 1 Abbreviations: DTNB = 5,5′-dithiobis-(2-nitrobenzoic acid); DTT = dithiothreitol; IAA = iodoacetic acid; IAAm = iodoacetamide; NEM = N-ethylmaleimide; PHMB = p-hydroxymercuri-benzoate; SDS = sodium dodecyl sulfate. at 37 ° causes dissociation to subunits, followed by degradation to species sedimenting more slowly than the small subunit. During this treatment a reduction in sedimentation coefficient of the subunits is observed. Other thiol-blocking reagents were found to be less active, the order of reactivity being PHMB ⪢ DTNB ⪢ IAA > NEM > IAAm. The observation is not solely the result of ribonuclease damage caused by inactivation of a ribonuclease inhibitor, although a trace amount of ribonuclease activity which increases slightly in the presence of PHMB is associated with the ribosomes. Electrophoretic analysis of rRNA and hyperchromicity studies support this conclusion. It is suggested that when sulfhydryl groups are blocked, more slowly sedimenting species are formed which might be more sensitive to ribonuclease than were the native ribosomes.