Open AccessMicroenvironment of the binding site in the lac carrier protein.
Author(s) -
Shimon Schuldiner,
Rudolf Weil,
Dan E. Robertson,
H. Ronald Kaback
Publication year - 1977
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.74.5.1851
Subject(s) - chemistry , fluorescence , methylene , perchlorate , alkyl , quenching (fluorescence) , binding site , homologous series , escherichia coli , methylene blue , stereochemistry , crystallography , biochemistry , medicinal chemistry , organic chemistry , ion , physics , quantum mechanics , gene , photocatalysis , catalysis
Studies with a homologous series of (N-dansyl)aminoalkyl-1-thio-beta-D-galactopyranosides containing two to six methylene carbons bridging the galactosyl and dansyl ends of the molecules are described. The compounds were utilized in radioactive and nonradioactive form, and binding of each homologue to membrane vesicles isolated from Escherichia coli ML 308-225 was measured directly by flow dialysis in the presence of D-lactate. The results are compared with the D-lactate-induced fluorescence enhancement observed with each dansylgalactoside and with the ability of N-methylpicolinium perchlorate to quench the fluorescence of the bound homologues. The binding affinity of the lac carrier protein for the probes varies directly with the length of the alkyl linkage, and the same number of binding sites is observed with each homologue. In contrast, however, the increase in fluorescence observed upon binding varies dramatically as the alkyl chain is increased in length, with the fluorescence exhibiting maximal values at two and six methylene carbons and a minimum at four methylene carbons. Furthermore, quenching by N-methylpicolinium perchlorate exhibits an inverse relationship and maximum quenching is observed with the 4 carbon homologue. Possible reasons for this behavior are discussed.