Structual formation and structure-function relationship of protein studied with the use peptides

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In biosystems, proteins interact with each other. In this research, oligopeptides are used as models of the protein interacting site, and the interaction between the protein and the peptide is studied in detail. The following results are obtained.1. Cytochrome c(cyt c) was reduced by a tyrosine-containing peptide, tyrosyltyrosylphenylalanine (TyrTyrPhe), at pH 6.0-8.0. Cyt c was reduced at high peptide concentration, whereas the reaction did not occur effectively at low concentration. The reciprocal initial rate constant (1/k_<int>) increased linearly against the reciprocal peptide concentration and against the linear proton concentration, whereas log k_<int> decreased linearly against the root of the ionic strength. These results show that deprotonated (TyrTyrPhe)., presumably deprotonated at a tyrosine site, reduces cyt c by formation of an electrostatic complex.2. From the MALDI-TOF MS spectra of the reaction products obtained from the reaction between cyt c and YYF, formation of a … More quinone and other tyrosine derivatives of the peptide was supported. These products should have been produced from a tyrosyl radical. The results are interpreted that a cyt c_<ox>/(TyrTyrPhe)【tautomer】 cyt c_<red>/(TyrTyrPhe)・ equilibrium is formed, which is usually shifted to the left. This equilibrium may shift to the right by reaction of the produced tyrosyl radical with the tyrosine sites of unreacted TvrTvrPhe peptides.3. Oxidized plastocyanin (PC) was reduced with TyrTyrTyr at neutral pH. The reciprocal initial rate constant (1/k_<int>) increased linearly with the reciprocal TyrTyrTyr concentration and proton concentration. The results showed that PC was reduced by the deprotonated species of TyrTyrTyr. A linear increase of log k_<int> with increase in the ionic strength was observed due to decrease in the electrostatic repulsion between negatively charged PC and deprotonated (TyrTyrTyr).These results show that a metalloprotein could be reduced at neutral pH with a tyrosine-containing oligopeptide. Less