| The mineral and organic phase of cuticles of the penaeid shrimps, Fennero-penaeus chinensis and Litopenaeus vannamei, were studied comprehensively and systematically by the technologies of electrophoresis, Fourier transform infared spectroscopy (FTIR), X-ray diffraction (XRD) patterns and amino acid compositon analysis. The results are summarized as follows:According to the FTIR spectra, there are large contents of chitin and other kinds of polysaccharides in the whole cuticles. The chitin is α-chitin, whose characteristic bands appear at 3285 cm-1, 2962 cm-1, 2932 cm-1, 2885 cm-1. The bands at 1420 cm-1, 875 cm-1 are characteristic of calcite, so calcium carbonate crystals deposited in prawn cuticles mainly exists in calcite. FTIR analysis of soluble and insoluble proteins indicates Amide I bands occur at 1649-1652 cm-1, 1656-1658 cm-1, and Amide II bands present at 1649-1652 cm-1, 1656-1658 cm-1. It can be supposed that Amide I bands adopt α-helix conformation, while antiparallel (3-sheet and parallel (3-sheet structures are respectively reflected in Amide II band of soluble proteins and insoluble proteins. Compared with soluble proteins, insoluble proteins have Amide IV,V, VI bands , but no amide III. The bands at 993-995 cm-1 in insoluble proteins probably due to PO43-. From the results of X-ray diffraction analysis we found a large content of a-chitin mainly shows up as broad reflections at 9.6677A. and 4.4803A. Peaks at 3.0436A and 2.4967A are attributed to calcite. In Litopenaeus vannamei, the weak bands detected at d values of 3.4582A and 3.3803A may reflect the presence of aragonite or vaterite.Based on SDS-PAGE analysis, the soluble proteins are mostly proteins with low molecular weight (MW), ranging from 6 to 30 kDa, while insoluble proteins range between 20kDa and 60 kDa, whose lowest MW is higher than 11 kDa. In different growing stages and different kinds of penaeid shrimps, soluble and insoluble proteins have a little differences. About methods of purification, HC1 is a good choice forextracting soluble proteins with high and medium MW, whereas HAc and Tris are fit for low MW proteins. For insoluble proteins, EDTA-Urea is hard to purify the proteins with high MW, but SDS-DTT and mercaptoethanol-saturated guanidine hydrochloride are both efficient. From almost each soluble extract, three bands 20-2 IkDa, 16-18kDa and 14-15kDa, can be sepatated, and in almost each insoluble extract, six bands can be detected, 60-65kDa, 44-48kDa, 33-36kDa, 29-32kDa and 17-20kDa (two bands).Amino acid composition analysis shows that Cys can not be detected in soluble and insoluble proteins from cuticles of penaeid shrimps, and Met content is lower than 1%. Large contents of small side-chain amino acid (Ala and Gly, 24-26%) and acidic amino acid (Asn and Glu, 24-27%) are found in soluble proteins, whose hydroxyl amino acid (Ser and Thr, 11-13%) is relatively high. For the insoluble proteins, content of acidic amino acid (Asn and Glu, 17-19%) is apparently lower than that of soluble proteins, while the content of hydrophobic amino acids is higher than that of soluble proteins.
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