Study On The Mechanism Of Penicillin Binding Milk Protein

Nowadays penicillin is one of the most common antibiotics used to treat cows with mastitis. After milk cow taking drug, partial penicillin enters into the mamma of milk cow by blood circulation and forms a kind of steady static compound in the cow’s milk. Penicillin residues in milk will not only have a serious effect on the quality of dairy product, bring about economic loss in the dairy processing, but also cause anaphylactic reaction in some people who are naphylaxis. At the same time, drinking dairy products with antibiotics residues for a long time will cause unbalance flora, drug tolerance and human immunity declining. So the research on the binding mechanisms of penicillin and milk protein has a significant role on dairy safety and sanity.Ultrafiltration, fluorescent spectroscopy, CD spectroscopy and synchronous fluorescence technology were firstly applied in this paper to study the binding mechanism of penicillin and milk protein. The main contents included:1. In order to determine the binding rate by HPLC after centrifugal ultrafiltration, penicillin was mixed with skim milk, casein and whey protein respectively, and incubated in pH6.6,37℃ water bath. The binding time was obtained at the same time. Casein (a-casein and β-casein) and bovine serum albumin were the main penicillin binding components in milk. Penicillin binding rate with skim milk was not affected by pasteurization, but would rise after UHT.2. The interaction of penicillin with a-casein, β-casein and bovine serum albumin was analysed respectively by fluorescent method. Data was analysed according to Stem-Volmer equation and Double logarithmic equation by penicillin had quenching effect on protein fluorescent sources. Compared with quenching rate constants in the different temperature, then penicillin arised static quenching process and form steady non-fluorescent ground state composite with three protein accounted above was determined. The binding constant and number of binding site of binding reaction were obtained.3. Thermodynamic parameters of penicillin binding a-casein, β-casein and bovine serum albumin were obtained by double logarithmic equation and modifying Stern-Volmer equation. It proved that hydrogen bond was the main interaction force of penicillin with bovine serum albumin and α-casein and electrostatic attraction was the main interaction force of penicillin with β-casein. According to Foster fluorescence resonance energy transfer theory, the binding space of the interaction of penicillin and three protein accounted above was figured out. Further existence of static mechanism was determined in the reaction process.4. It was found that fluorescence of tryptophan residue was quenched in the interaction of penicillin with bovine serum albumin and a-casein and tyrosine residue was quenched in the interaction of penicillin with β-casein by Synchronous Fluorescence. The polarity and hydrophobicity of amino-acid residues would be changed. The study about penicillin binding a-casein, β-casein and bovine serum albumin by CD spectroscopy proved that the binding of penicillin and protein would change the protein conformation. It was further explained that penicillin and protein form steady compound in the cow’s milk.