Oriented protein in chitinous structures.

Abstract

THE chaetae of Aphrodite aculeata, a large errant polychaete, lose upwards of 65 per cent of their weight on extraction with 10 per cent potash or diaphanol. The surviving transparent bristle consists of chitin (polyacetylglucosamine). The alkali extract of alcohol-fixed bristles gives the colour reactions of certain amino-acids—of tryptophane, for example—suggesting the presence of protein1, and Dr. C. H. Brown (who kindly examined for us fresh material from the related genus Hermione) has obtained positive Millon and arginine and negative cystine reactions. Swelling tests show that salt-linkages and S—S linkages play but little part in determining the stability of the material, while the complete solubility of both Hermione and Aphrodite bristles in 10 per cent aqueous sodium hypochlorite suggests that the material removed by potassium hydroxide or diaphanol is an aromatically tanned protein. Sections of the base of Hermione chaetae gave positive argentaffin and diazo reactions—indicative of the presence of dihydroxyphenols2. These results agree with those of recent work on the chaetae of the earth-worm, Allolobophora longa3.