Expression of human placental ribonuclease inhibitor in Escherichia coli

Human placental ribonuclease inhibitor (PRI) has been expressed in and isolated from Escherichia coli. Its apparent molecular weight, immunoreactivity and amino acid composition are virtually identical with those of native PRI. It inhibits the enzymatic activities of either angiogenin, a blood vessel inducing protein homologous to pancreatic RNase (RNase A), or RNase A in a stoichiometry of 1:1. Recombinant PRI binds to angiogenin and RNase A with Ki values of 2.9 x 10(-16) M and 6.8 x 10(-14) M, respectively, comparable to the affinities of native PRI for these enzymes. Thus, these results confirm that PRI inhibits angiogenin more effectively than RNase A.