Variations of ecdysone titer and hemolymph major proteins during the molt cycle of the spider crab Acanthonyx lunulatus
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The present study was undertaken to clarify the minimum level of digested protein required to induce larval molting. Newly-ecdysed fourth-instar larvae of Bombyx mori were reared on semi-synthetic diets containing various doses of protein (5 to 20%, dry weight basis), and the coefficient of digestibility as well as the ecdysteroid level of larval hemolymph was determined. According to the decrease in dietary protein, the ecdysteroid level of hemolymph lowered and the minimum dietary level of protein required to induce molting was found to be 7%. The ecdysteroid level of hemolymph increased when the amount of digested protein exceeded 18mg per larva during the 4th instar. When the protein amount exceeded 19mg, the larvae molted. Larvae reared on a 5% protein diet survived more than 20 days and died without molting. With a 5% protein diet, no increase was recognized in the ecdysteroid level of the larval hemolymph. But when the larvae were fed on a commercial diet in place of the P5-diet, the ecdysteroid level increased, and the larvae were able to molt.
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The in vivo oxygen-binding characteristics of Cancer magister whole hemolymph were compared across developmental stages with those of purified hemocyanin. When the 25S hemocyanins from first-instar juvenile and adult C. magister were dialyzed against first-instar juvenile saline, the P50 values at pH 7.8 differed by 54 %: 2.16 kPa for the adult and 4.68 kPa for the first-instar juvenile. Since both purified proteins were examined under identical conditions, this represents an intrinsic stage-specific difference in hemocyanin O2-affinity. When the two types of hemocyanin were dialyzed against their respective stage-specific salines, the oxygen affinities differed by only 28 %: 3.39 kPa for the adult and still 4.68 kPa for the first-instar juvenile. Thus, the intrinsic difference in hemocyanin O2-affinity was reduced by the stage-specific differences in hemolymph ion concentrations. Even more significant is the fact that the whole-hemolymph P50 values of the juvenile and adult were indistinguishable at in vivo pH and divalent cation levels specific for each stage. Thus, despite significant differences in the intrinsic oxygen affinity of the purified 25S hemocyanin during development, the whole-hemolymph oxygen-binding properties are conserved. In the juvenile crab, it appears that the low-affinity hemocyanin serves to modulate the effects of a weak renal regulation of [Mg2+]. As ion regulation is enhanced during development and divalent cation levels decrease, the crab synthesizes higher-affinity hemocyanin.
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The molting cycle of Penaeus vannamei juveniles was characterized by distinct and predictable changes in the setae of pleopods. The molt pattern was diecdysic with a relatively short intermolt period (40%) and a long proecdysial period (>53%). The levels of both total protein and ecdysteroids increased in the hemolymph during proecdysis, whereas the level of hemolymph glucose was low at metecdysis and proecdysis and maximal during anecdysis. As revealed by SDS-PAGE, the relative concentrations of two polypeptides (32 kD; 175 kD) changed during the molting cycle.
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