Identification of a substrate site for liver transglutaminase on the aminopropeptide of type III collagen.

The aminopropeptide of type III collagen incorporates [3H]putrescine in the presence of liver transglutaminase, and the change in incorporation with concentration indicates one binding site on each of the Mr = 15,000 subunits of the peptide. At low concentrations the incorporation was comparable to that of dimethyl casein and much greater than actin or fibrinogen. Cleavage and Edman degradation of the aminopropeptide identified the major putrescine-binding site as glutamine in position 14. The surrounding amino acid sequence (Leu-Gly-Gln-Ser) shows homology with some synthetic peptide substrates of transglutaminase.