Ribonuclease inhibitor which inhibits RNASE1, RNASE2 and ANG. May play a role in redox homeostasis. Forms high-affinity heterodimers with RNASE1, ANG and RNASE2. The LRR domain forms a horseshoe-shaped structure that interacts tightly with target RNases via a large protein interaction surface on its interior side. The N-terminus is blocked. At least 30 of the 32 cysteine residues are in the reduced form.