Enzymatic analysis of carbohydrate metabolism in Strongylocentrotus purpuratus larvae during laboratory experiments with different food treatments

Strongylocentrotus purpuratus (Stimpson 1857) originally collected in November 2022 from La Jolla, USA (Lat: 32.842674; Long: -117.257767) were held in flow-through tanks which were filled with water from Kiel Fjord adjusted to 31.5 psu in the Christian-Albrechts-Universität zu Kiel at 10 °C. For experimental characterization of carbohydrate digestion between September and November 2023 S. purpuratus larvae were generated by gently shaking adult males and females and held in climate chambers at 15°C and 31.5 psu up to 10 days under two different food conditions. Carbohydrate-degrading enzymatic activity against various substrates (starch, laminarin, cellulose, xylan, trehalose) was assessed using 3,5-dinitrosalicylic acid (DNS, Miller, 1959). The activities of degradation were quantified by measuring the rate of reducing sugar production resulting from the hydrolysis of soluble starch, carboxymethylcellulose sodium salt (medium viscosity), laminarin from Laminaria digitata, xylan and D-(+)-Trehalose dihydrate. For all reactions the amount of reducing sugar was determined spectrophotometrically at 540 nm with glucose as the standard (xylose for xylan characterization) by first determining the difference between positive reaction and negative controls for t₀ and t₁ and then determining the difference t₁ - t₀. Finally, this was set in relation to the amount of protein used and the reaction time, so that the results could be in pmol reducing sugars mg protein⁻¹ h⁻¹.