Abstract
D/L aspartic acid values from a 350-year time series of annual growth bands of a living colony of the coral Porites australiensis show a very regular pattern of increase with age. The initial rate of racemization is extraordinarily rapid (0.6% per year) but slows in older growth bands to 0.04% per year (4% per century). The skeletal proteins show progressive hydrolysis with increasing age, with free aspartic acid comprising 16% of the total aspartic acid in the 350-year-old band. The proteins are unusually rich in aspartic acid (nearly 50 mol%). The relative weakness of the peptide bonds formed by aspartic acid moieties is probably responsible for the rapid hydrolysis and consequent rapid racemization of aspartic acid. Racemization analysis provides a means for checking for sections of missing bands in corals and for screening of prospective samples for U-Th dating.
Highlights
RECENTSTUDIESHAVEshown that aspartic acid has a high rate of racemization in mollusk shells during the first few centuries following formation of the shell (GOODFRIENDet al., 1991; GOODFRIEND, 1992)
The results presented here are based on a 350-year time series of samples from a core cut through a large head of the coral Porites australiensis from the Great Barrier Reef, Queensland, Australia
The very high aspartic acid content of the coral proteins is likely responsible for the rapid hydrolysis
Summary
Geochimrca a Cmmochimica AC@ Voi. 56, pp. 3847-3850 Copyright 0 1992 Pergamon Press Ltd. 3847-3850 Copyright 0 1992 Pergamon Press Ltd. Printed in U.S.A. Aspartic acid racemization and protein diagenesis in corals over the last 350 years. Abstract-D/L aspartic acid values from a 350-year time series of annual growth bands of a living colony of the coral Porites australiensis show a very regular pattern of increase with age. The initial rate of racemization is extraordinarily rapid (0.6% per year) but slows in older growth bands to 0.04% per year (4% per century). The skeletal proteins show progressive hydrolysis with increasing age, with free aspartic acid comprising 16% of the total aspartic acid in the 350-year-old band. The proteins are unusually rich in aspartic acid (nearly 50 mol%). The relative weakness of the peptide bonds formed by aspartic acid moieties is probably responsible for the rapid hydrolysis and consequent rapid ~cemization of aspartic acid. The relative weakness of the peptide bonds formed by aspartic acid moieties is probably responsible for the rapid hydrolysis and consequent rapid ~cemization of aspartic acid. summation analysis provides a means for checking for sections of missing bands in corals and for screening of prospective samples for U-Th dating
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