| Abstract: The pepsin is the main digestive ferment in animal, which have stronger uniqueness in the gastric juice, it catalysis the peptide hydrolysis consisted by Phe, Tyr and Trp, making the protein turn into smaller polypeptide. As an important protease, pepsin s enzymic nature, substrate uniqueness, inhibition, et al. are different from other protease, therefore it has theoretical research value and applied value. The alkaloid is a kind of alkali natural organic containing nitrogen heterocyclic compound, which exist in the plant extensively, there are many important applications on medicine. Based on alkaloid medical value, in view of the method of developed spectral analysis this article discussed the interaction between three kinds of alkaloid and pepsin in recent years. Through the effect of three kinds of alkaloid on pepsin enzyme kinetics and interactive ultraviolet spectrum and fluorescence spectrum of the pepsin, we inferred the change and act mechanism of pepsin under influence of three kinds of alkaloid.First we study nature of the pepsin by adopting 2000 pharmacopoeia .we make substrate with the hemoglobin, determining the pepsin activity with ultraviolet spectrum under 275nm, enzyme hydrolysis hemoglobin turn into a umol tyrosine as a activity unit with every minute, using hemoglobin as the substrate and study enzymes property , get Km value is 0. 86mmol/L, the optimum temperature is 40℃, the optimum pH2. 0.It is found that the effect of camptothecin, colchicine , puerarin on pepsin enzyme kinetics exhibited inhibition , the inhibition dynamics of three kinds of alkaloid in pepsin is made respectively under the different concentration. The result is that: the ki of camptothecin is 0.63 × 10-3 mol/L,the ki of colchicines is 0.976 × 10-3mol/L, the ki of puerarin is 1.78 ×10-3 mol/L, Three kinds of alkaloid belong to in-competition type of inhibitor. The order of inhibition ability is: camptothecin > colchicine > puerarin.Through making ultraviolet spectrum concentration and time difference table with the pepsin respectively under 200-400nm to camptothecin , colchicine and puerarin, we found the ratio of mole to concentration is 3:1 between camptothecin ,colchicine and pepsin, the ratio of mole to concentration is 4:1 between puerarin and pepsin have most obvious ultraviolet spectrum absorb . Discover the influence of acting time to three kinds of alkaloid at the same time and pepsin interact system is not big, its combination may be an instantaneous course.Through making the fluorescence emission spectrum under room and 37°C to study the pepsin respectively under 300-400nm to camptothecin , colchicines and puerarin, we found three kinds of alkaloid have fluorescence quenching to the pepsin, The kq is calculated according to the stern-volmer equation, get kq of camptothecin to pepsin is 1. 239X 10u(mol/L)'-S', kq of colchicines to pepsin is 1.059 X 1013(mol/L) ' ■S' , kq of puerarin to pepsin is 0. 669 X10" (mol/L) ' S ' . It may infer that the fluorescence influence of three kinds of alkaloid on pepsin may a static mechanism of fluorescence quench.
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