Blood sugars in relation to chitin synthesis during cuticle formation in Emerita asiatica

Abstract

Blood sugars of the crustacean Emerita asiatica were studied during the moult cycle to examine their possible role in the synthesis of chitin, which takes place at the time of moulting. Blood sugars occur both in free state as well as bound with proteins, and show quantitative fluctuations in different phases of the moult cycle. The values of sugars were estimated in relation to total blood volume, to obviate the effects o absorption of water and consequent dilution of blood taking place during moulting. The data obtained suggest that the presence of glucosamine only during premoult stage may be due to resorption of chitin preparatory to the shedding of the cuticle. The fluctuations in the protein-bound blood sugars appear significant in the context of the synthesis of chitin, in view of the correlation seen between these and the chitin content. The above suggestion is supported by the observation that they are not involved in the nutritive metabolism of the crustacean. The protein-bound sugars do not appear to undergo further changes in the blood, as may be inferred by the absence of uridine diphosphate, and uridine diphosphate acetylglucosamine compounds, which have been suggested to be the more immediate precursors of chitin during the moult cycle of insects. It is suggested that protein-bound sugars may be transported, as such, to the epidermis, which may be the site of the final steps in chitin synthesis.