Aspartic acid racemization and amino acid composition of the organic endoskeleton of the deep-water colonial anemone Gerardia : Determination of longevity from kinetic experiments

Abstract

An age of 250 (±70) yr is estimated for a specimen of the colonial anemone Gerardia collected alive from 630 m depth off the Bahamas. This age is calculated from (1) the difference in aspartic acid (Asp) racemization measured in the outermost (youngest) and innermost (oldest) layers of the trunk of the organic endoskeleton of the specimen and (2) the estimated rate of Asp racenlization, as extrapolated from heating experiments. A progressive increase in D/L Asp values was observed from the outermost (0.052) to the innermost (0.099) layer of the trunk. Asp racemization rates determined at 60, 80, and 100°C in the laboratory were used to determine the Arrhenius parameters, from which the rate at present ambient temperature (12.5°C) was calculated. The activation energy of Asp racemization was estimated to be 29.1 kcal/mol. The estimated age (250 yr) is much younger than that suggested by radiocarbon measurements of the specimen (ca. 1800 yr). The amino acid composition of the endoskeleton of Gerardia is unusual, with histidine comprising 30% of the total. The composition resembles proteins of the endoskeleton of antipatharians (black corals).