pLactoyl-pepstatin (an acylated tetrapeptide) is much more readily soluble in aqueous media than the more common isovaleryl- and acetyl-pepstatins (acylated pentapeptides). However, the K1 value for inhibition of cathepsin D by lactoyl-pepstatin at pH 3.5 is approx. 10(-7) M, some two to three orders of magnitude weaker than has been obtained previously for isovaleryl- or acetyl-pepstatins. One of the peptides released during activation of pig pepsinogen is known to be an effective inhibitor of pig pepsin, but it does not alter the activity of the similar aspartic proteinase, pig cathepsin D./p
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