Studies On The Interaction Between Dipeptides Contained Proline Or Polar Dipeptides With Metal Ions

As the smallest peptide unit, dipeptides are the building blocks of protein andcondensated with two amino acids. Moreover, dipeptide widely exists in nature andis easy to use and prepare. In the organism, metal ion rarely exist in the form of freeions, mostly to form complexes with proteins、nucleic acids or other biologicalmacromolecules, which participate in the process of life. Among the known biologicalenzyme as well as protein, about1/3of them play an active or structural center role incontrolling various biological function with the metal ions. However, due to thediversity and complexity of protein structure, there are a lot of difficulties for studyingit directly. Therefore metal complexes of dipeptides have been selected as simplemodel compounds for studying protein–metal ion interactions. In this paper, theinteraction of plasmid pUC19DNA with8peptides which contains proline in theabsence or in the presence of Cu(II)、Zn(II)、Co(II)、Ca(II)、Mg(II) complexesrespectively were studied. At the same time, the interaction of11polar dipeptides andmetal ions were investigated by NMR titration.First, the cleavage reaction of supercoiled pUC19DNA promoted by8proline-contained dipeptides was investigated in the presence of Cu(II)、Zn(II)、Co(II)、Ca(n)、Mg(II). The results indicated that supercoiled DNA (Form I) could bedegraded to relaxed circular DNA (Form II) in the presence of Co(II) ion. Meanwhile,the optimum conditions on the cleavage of pUC19DNA by dipeptides and metal ionswere investigated from buffer, pH value, concentration and reaction time.The test results showed that the optimal conditions for DNA cleavage by dipeptidesand Co2+is pH6.8or7.0, concentration0.6mM/L, and time48h. Moreover,experiment also proves that proline-contained dipeptides can cleave DNA via thehydrolysis pathway.Second, the interaction of proline-contained dipeptides with metal ions wasexamined by UV, and the association constant has been calculated. The absorbance ofthe dipeptides system undergoes a distinct increase and red shift when the metal ionsaddes. The results showed that the binding ability of proline-contained dipeptides with Co2+was stronger than other metal ions. Furthermore，the CT-DNA binding ability ofthe dipeptides and metal ions was studied by evaluating the absorbance intensity ofthe DNA system upon the addition of the two compounds, respectively.At last,the interaction of11polar dipeptides with4metal ions (Li+、Cu2+、Zn2+、Co2+) was examined by NMR，and the association constants (Ka) of these polardipeptides with Li+was acquired. The results showed that the stoichiometric ratiobetween dipeptides and Li+was1:1，and L-Glu-L-Glu had stronger binding abilitywith Li+ions than other dipeptides. Moreover，it was found that the interactionbetween polar dipeptides and divalent metal ions carried out in two stages.