Studies onthe chemical nature of lysine-binding sites and on their localization in human plasminogen

The isolated 'kringle' structures 1 and 4 of human plasminogen lost lysine affinity upon photo-oxidation of histidine, but mostly retained it in the presence of 6-aminohexanoic acid. Lysine affinity was lost and could be partially restored after blocking of histidine with diethylpyrocarbonate and deblocking, or after esterification of COOH-groups and saponification. Only His-31 and most likely Asp-54 qualify as participants in a lysine binding site when the primary structures of the 'kringles' are considered.