The protein of brachiopod shell–II. Shell protein from fossil articulates: Amino acid composition

Abstract

1. 1. Proteinaceous fragments have been obtained by decalcifying fossil Jurassic and Silurian brachiopod shells with ethylenediaminetetraacetic acid (disodium salt), showing that polypeptide chains have survived through distant geological time. Their amino acid compositions yielded on hydrolysis are presented. 2. 2. They show marked differences from the nearest Recent relatives, a survey of the shell protein amino acid compositions of which has shown a basis for a structural protein taxonomy. Some differences are related to the composition of the harder protein layers within a Recent shell, and may reflect ageing and hardening processes and perhaps greater resistance to degradation of shell with matured protein. Other differences, particularly raised serine and glutamic acid values, are unrelated to the composition of the hard protein layer and have been widely observed in fossil material of other phyla; they are probably effects due to long geological time, perhaps thermodynamic. 3. 3. There are hints from some amino acid data that all phylogenetic information may not be lost in fossil material, though to recover it the effects noted above must be eliminated. Many more data are needed on amino acid compositions and also from peptide mapping to establish persistently recurring amino acid groupings.