Specific dose-dependent 125I-labeled Lys-plasminogen-binding (A) and 125I-labeled Glu-plasminogen-binding (B) activity of streptococcal wild-type strain D471-M6, isogenic mutant strain D471-M6-SEN-K434-435L, and the wild-type strain containing the spectinomycin resistance gene, D471-M6-aad. Each point represents the mean of three independent experiments, each carried out with duplicate samples, ± the standard error of the mean. The specific amount of plasminogen bound was determined on the basis of the specific activity of the 125I-labeled plasminogen added. N.S., no statistically significant difference (P > 0.05).