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The transglutaminase-catalysed incorporation of primary amines (putrescine and monodansylcadaverine) into bovine beta-lactoglobulin has been studied. In the presence of 1 mM-dithiothreitol between 1 and 2 mol of amine can be incorporated per mol of beta-lactoglobulin subunit. There is very little incorporation of amines in the absence of reducing agent. By isolating and sequencing the modified peptides, the sites of modification have been identified as Gln-159 (preferred) and Gln-155. C.d. has been used to study the structure of beta-lactoglobulin over a range of pH values and in the presence or absence of dithiothreitol. The results are discussed in terms of the X-ray-crystallographically determined structure of beta-lactoglobulin.

The transglutaminase-catalysed incorporation of putrescine and monodansylcadaverine into yeast phosphoglycerate kinase has been studied. There is little incorporation of the amines into wild-type enzyme, but nearly stoichiometric incorporation into the histidine-388----glutamine mutant enzyme. C.d. studies show that the overall structure of the mutant enzyme is very similar to that of the wild-type enzyme. Incorporation of the amines into the mutant enzyme causes no significant change in its activity. Glutamine-388 was shown, by isolation and sequencing of the modified peptide, to be the site of incorporation of monodansylcadaverine into the mutant enzyme. The specificity of the transglutaminase reaction is discussed in the light of available data.