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Levine JD, Gordon NC, Bornstein JC, Fields HL.Levine JD, et al.Proc Natl Acad Sci U S A. 1979 Jul;76(7):3528-31. doi: 10.1073/pnas.76.7.3528.Proc Natl Acad Sci U S A. 1979.PMID: 291020Free PMC article.