In vitro conversion of proinsulin to insulin by cathepsin B in isolated islets and its inhibition by cathepsin B antibodies.

Purified bovine cathepsin B, when incubated with isolated rat islets of Langerhans, completely converts proinsulin to insulin as demonstrated by the incorporation of 14C-leucine into islet proteins, releasing lysine as the only basic amino acid. Cathepsin B antibodies raised in rabbit inhibited the above conversion.