Specific for human proinsulin (site of connection of C-peptide and C-end of B-chain of proinsulin molecule), Kd 1.1 x 10-8 M. Not cross-reacts with human, bovine and porcine insulin, bovine and porcine proinsulin, and human C-peptide. Can be used for detection of human proinsulin in two-site enzyme immunoassay, recommended pairs (coating - conjugate): 3A1 - 7F8 Hytest Cat.# 2I1; for immunohistochemistry on frozen sections.