Competition of murine GPIIIa N-termini containing substitution mutations with the HPA-1a–positive human GPIIIa N-terminus. In an ELISA, murine substitution mutations were tested for their ability to compete with the human HPA-1a containing 66 amino acid segment. An antiserum was incubated with various murine GPIIIa N-termini containing substitution mutations before being assayed with the human N-terminal segment. Due to the numerous samples, the results were separated into three groups. Some samples are present in more than one group. In (A), substitution mutations (m3a_32,33and m3a_22,30,32) were tested for their ability to compete with the human GPIIIa N-terminal segment. The results in graph (B) compare the ability of the murine proteins with substitutions at position 30 to compete with the human segment; those in graph (C) compare the ability of the murine proteins with substitutions at position 39 to compete. The legend for the substitution mutations is given (bottom, right).