Analysis of Endogenous Semicarbazide during the Whole Growth Cycle of Litopenaeus vannamei and Its Possible Biosynthetic Pathway.

This research aims to analyze the biosynthetic pathway of endogenous semicarbazide (SEM) in shrimps using Litopenaeus vannamei as the model target. To achieve this objective, the content of SEM in L. vannamei throughout the whole growth cycle was monitored under the strict control of external environmental interference. Experimental results showed that SEM was found in the shrimp shell at all stages, with its content decreasing first and then increasing, and no SEM was detected in the shrimp muscle of each growth stage. This indicated that endogenous SEM in L. vannamei was derived from the shrimp shell. At the same time, the content of amino acids in the shrimp shell and the corresponding substances involved in the urea cycle in the entire growth cycle of shrimp were monitored. The correlation analysis between them and the changes in the SEM content in shrimp showed that arginine had the largest correlation coefficient (0.952) with the changes in the SEM content. The main substances of the urea cycle may be related to the production of SEM. In combination with the water environmental test of high ammonia nitrogen, it was presumed that the formation of endogenous SEM was related to the amidine group of arginine and amide structure of citrulline and urea. Arginine, citrulline, and urea in the urea cycle of L. vannamei eventually produced SEM via an oxaziridine intermediate under the action of hydrogen peroxide and ammonia, and a standardized reaction test was conducted to verify the hypothesis and, thus, provided a new idea for future endogenous SEM research.