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Helfrich-Förster C.Helfrich-Förster C.Proc Natl Acad Sci U S A. 1995 Jan 17;92(2):612-6. doi: 10.1073/pnas.92.2.612.Proc Natl Acad Sci U S A. 1995.PMID: 7831339Free PMC article.