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Challita PM, Kohn DB.Challita PM, et al.Proc Natl Acad Sci U S A. 1994 Mar 29;91(7):2567-71. doi: 10.1073/pnas.91.7.2567.Proc Natl Acad Sci U S A. 1994.PMID: 8146155Free PMC article.