The effects of lactoyl-pepstatin and the pepsin inhibitor peptide on pig cathepsin D.

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Abstract
Lactoyl-pepstation [Streptomyces] (an acylated tetrapeptide) is much more readily soluble in aqueous media than the more common isovaleryl- and acetyl-pepstatins (acylated pentapeptides). However, the Ki value for inhibition of cathepsin D by lactoyl-pepstatin at pH 3.5 is .apprx. 10-7 M, some 2-3 orders of magnitude weaker than was 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.