The Bingding Mechanism And The Effecton Digestive Function Of Four Small Molecules To Pepsin

In recent years,with the rapid development of China's economy,the improvement of production capacity and living standards,the proportion of semi-health in China's population has grown rapidly.People are paying more and more attention to food and drug safety.The bind of small molecules such as drugs interact to biological macromolecules such as proteins can affect the activity and structure of proteins,and thus can adjust various functions of the human body.It is closely related to human health.In this paper,using pepsin?PEP?,the main digestive enzymes in the human body,and several small molecules as the research subjects.Their binding mechanisms were studied in detail by various methods,and their effects on human safety were discussed.The research content is divided into the following parts:Chapter one:Several common spectral methods to investigate drug-protein interact systems have been summarized,and the latest developments in the field of drug-protein interaction have been introduced.A total of 44 references were cited.Chapter two:Under simulated physiological conditions,fluorescence and synchronous fluorescence methods,UV,circular dichroism spectroscopy,and molecular docking techniques were used to study the combined mechanism between pepsin and gliclazide?GCZ?,a hypoglycemic agent,at three temperatures,298 K,310 K and 318 K.The experimental results showed that the drug molecule can form a stable complex with PEP in a ratio of 1:1,so that the endogenous fluorescence of PEP is quenched,and the conformation of PEP is changed.The content of?-helix in the structure is decreased from 21.13%to 20.16%.Using the binding constant K_a of GCZ and PEP reaction and the number n of binding sites,the formula of the binding rate of GCZ and PEP was deduced.According to the formula,the situation of GCZ in gastric juice reacted with PEP was calculated.When a patient takes 40 mg of GCZ,the bind of GCZ and PEP will reduce the PEP in the gastric juice by 96.69%,that is,the oral GCZ will affect the patient's digestive function.Molecular docking result indicated that the binding position of GCZ is located at the active center of PEP,and the interaction between them is driven by electrostatic attraction and hydrogen bonding forces.The above series of conclusions showed that the use of spectroscopy to study the interaction of drugs and protein molecules is a systematic and comprehensive method.Chapter three:Using PEP spectrum as the detection object,the interaction mechanism between the hypotensor drug nifedipine?NDP?and PEP was still studied by varies spectroscopy methods and molecular docking technology.The experimental results showed that NDP mainly quenched the fluorescence of PEP,but this process was dynamic caused by intermolecular diffusion and collision,and at the same time,no significant changes in the secondary structure of PEP.The protein binding rate?W?of NDP measured at 310 K was71.79%⁸9.15%,and a binding rate model of NDP and PEP was established,W=-0.1273R²-0.0519R+0.8973.Hill's coefficients were approximately 1,which showed that the interaction of NDP and PEP will not affect the binding of subsequent drug to the protein.The molecular docking technique was used to simulate the interaction between NDP and PEP,the results demonstrated that the binding site of NDP is located in the active center of pepsin,which was consistent with the conclusion of the spectroscopic method,and it was also proved that the interaction of PEP-NDP system was driven by hydrophobic and hydrogen bonding.Chapter four:Using PEP spectrum as the detection object,the mechanism of interaction between cefonicid sodium?CFS?and PEP under optimum conditions was investigated by fluorescence and synchronous fluorescence method at three temperatures,298 K,310 K and318 K.Cefoncid sodium quenched the intrinsic fluorescence of pepsin at pH of 2.0 to form a new complex in a 1:1 binding mode driven by Van der Waals and hydrogen bonds.Hill coefficient was also used to investigate the drug synergy of CFS sodium and PEP,and the positive result was obtained.The protein binding rates of CFS in gastric juice was calculated and the binding model was established.It is concluded that about 21.41%to 24.54%of the protein in the blood was involved in the transportation of the drug during normal administration;if CFS is taken orally,almost all of the PEP in the stomach was consumed.The results obtained by fluorescence quenching method and synchronous fluorescence method were compared,and the conclusions and mechanisms were consistent.Chapter five:Using PEP spectrum as the detection object,the binding mechanism of sunset yellow?SY?on pepsin?PEP?were studied by fluorescence quenching method,synchronous fluorescence method and molecular docking technique.The results showed that SY can effectively quench the endogenous fluorescence of PEP.A 1:1 stable complex with a binding constant of 10⁴ was formed by SY and PEP.The binding site of SY located in the active center of the PEP and the binding was driven by electrostatic attraction and hydrogen bonding,thereby changed the conformation of PEP.The binding rate of SY was 2.45%¹.35%at 310 K,and the binding rate model was W?Q?=5.538×10^-6R²-5.188×10^-4R+0.02494.The binding rate of the PEP was 2.45%⁴7.11%,the binding rate model was W?B?=-2.271×10^-4R²+0.02103R+0.009030.Through estimation,it can be seen that when SY was set at the maximum intake of 0.0025 g at every time,it would reduce the PEP in gastric juice by58.79%,theoretically proved that SY has side effects on human digestive ability,and expanded the field of interaction between small molecules and proteins.