text: -CH-) has replaced a peptide bond in the peptide analogue sequence. To some extent the chemical structure of phosphinic peptides is similar to that of intermediates which are produced in hydrolysis of peptides by proteolytic enzymes. The hypothesis has been made that these pseudo-peptides mimic the structure of the enzyme substrates in their transition state and crystallography of zinc proteases in complex with phosphinic peptides supports that hypothesis.