Study On The Structure And Properties Of Collagen From Body Wall Of Urechis Unicinctus

Urechis unicinctus is one of the most important fishery resources in China,which has the high economic, nutritional and medicinal value. The distribution andmorphology of collagen fiber is studied from body wall of Urechis unicinctus, fromwhich, collagen is isolated to investigate the molecular structure and properties.1. Histological observation clarifies the presence of collagen fiber from thebody wall of Urechis unicinctus, but there is no muscle fiber from it. Collge fiber isnot bind to muscle fiber.2. Acid-soluble collagen is extracted from the body wall of Urechis unicinctus.Ultraviolet spectrum analysis shows that the feature absorption wavelength of ASC is228nm suggesting it is a typical collagen. Amino acid composition analysis furtherindicates that ASC is a typical type Ⅰcollagen. SDS polyacrylamide gelelectrophoresis suggests that ASC contained two alpha chains, β and γ chains. Itcontains disulfide bond. Fourier-transform infrared investigation shows the existenceof helical arrangements of collagen. The thermal denaturation temperature and thethermal shrinkable temperature are33.6℃and67.5℃.3. The rheological properties and functional characteristics of ASC aredetermined. Results indicates that the increase of frequency brings about the increaseof both storage modulus and loss modulus significantly at different concentration anddifferent temperature of collagen solution in the given frequency range. Collagenbehave is mainly viscous which is in terminal zone at low frequency and is mainlyelastic which is in plateau zone at higher frequency. Entanglements could be viewedwhen the concentration of collagen solution is higher, as well as the temperaturereaching40and50℃. But there are no significant entanglements in collagen solutionat the temperature of30℃. On the other hand, the functional properties of collagenfrom body wall of Urechis unicinctus are evaluated. Functional characteristics ofcollagen show that it has good emulsification and emulsion stability. 4. Scanning electron microscopy of the acid-soluble collagen shows a structureof filamentary fibril with helical arrangements. The distance between the molecularchains is1.14nm, and the unit height, typical of the triple helical structure, is0.27nm.Peptide mapping reveals that the collagen exhibits the homology with thegi/19556967, peptide matching degree can be up to39%.5. Aggregation kinetics of collagen from body wall of Urechis unicinctus isstudied. The main factors including mass concentration of collagen, pH value andionic strength, which affect the aggregation property, are discussed. The results provethat the aggregation characterization of collagen is closely related to the factorsmentioned above. When mass concentration of collagen is increased to1g/L, evidentaggregation behavior is found in solution. And collagen shows higher aggregation rateat pH7.4. Ionic strength slows down the collagen aggregation, but when the NaClconcentration reaching30or60mmol/L, it is easier to form large aggregates.6. The aggregation behavior of collagen from body wall of Urechis unicinctusis investigated by the pyrene fluorescence probe. The aggregation property ofcollagen shows the threshold mass concentration is found, namely the criticalaggregation mass concentration (CAMC). Using plots of pyrene I1/I3ratio versuslogarithm of different mass concentration of collagen, the CAMC is found to be at0.75g/L.