While preparing human placenta elongation factor 2 (EF-2), whose purification and some molecular properties are reported, we noticed the presence of numerous protein fractions which did not have EF-2 activity, but were ADP-ribosylated by diphtheria toxin in the presence of NAD+. All these proteins, like EF-2, were selectively retained by a heparin-Sepharose column, which we used as an affinity-chromatography step. This was also observed when EF-2 was prepared, by this purification step, from other sources, i.e. ox liver and two species of yeasts. In order to assess whether these proteins were a degradation product of EF-2, independent proteins or a mixture of both, they were analysed by subjecting them, after [14C]ADP-ribosylation, to exhaustive trypsinolysis. Only one radioactive peptide was found, thus suggesting that those proteins originate from EF-2 by some proteolytic process. Our findings indicate that this proteolysis does not occur after cell disruption, but is more or less active in the intact cell, depending on the system considered.

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