Abstract:The body wall of sea cucumber was hydrolyzed by five commercially available enzymes（neutral protease，alkaline protease，trypsin，papain，pepsin），respectively.The degree of hydrolysis（DH）and molecular weight distribution of the hydrolysates were determined，and the amino acid composition and structural properties of the fraction in the ultrafiltrate with molecular weight less than 3 kDa and its regulation of macrophages were investigated.The results showed that neutral protease had the strongest hydrolysis capacity（DH=17.18% in 300 min）.The fraction less than 3 kDa （SCH-N-I）accounted for 96.33% and the essential amino acids hit 89.52 mg/g in the hydrolysate prepared with neutral protease，which were higher than those in the hydrolysates yielded by the rest four proteases.According to the ultraviolet（UV）spectra and fluorescence spectra，SCH-N-I had higher surface hydrophobicity，UV absorption，and endogenous fluorescence intensity than fractions in ultrafiltrates yielded by other enzymes，and exhibited a red shift of the maximum absorption wavelength and the maximum intrinsic fluorescence，indicating that it might have higher immunobiological activity.The results of the macrophage immunoactivity assay showed that when the concentration of SCH-N-I was 200 μg/mL，macrophages demonstrated high survival rate[（121.79±4.98）% ]，strong phagocytosis（0.107 7±0.001 0），and high nitric oxide release[（15.39±0.33）μmol/L]in the LPS-induced immunization model.SCHN-I had higher immunoactivity than fractions in ultrafiltrates prepared with the rest four proteases.