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Porter AG, Smith JC, Emtage JS.Porter AG, et al. Among authors: emtage js.Proc Natl Acad Sci U S A. 1980 Sep;77(9):5074-8. doi: 10.1073/pnas.77.9.5074.Proc Natl Acad Sci U S A. 1980.PMID: 6254054Free PMC article.