Reaction of beta-lactoglobulin A and B with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole
Doperé, F.; Préaux, G.
Archives Internationales de Physiologie et de Biochimie 83(5): 962-964
1975
ISSN/ISBN: 0003-9799 PMID: 58622 Document Number: 85720
When 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) reacts with the amino or thiol groups of proteins, the N-NBD-derivatives show an absorption max. at 475 nm and the S-NBD-derivatives a max. at 425 nm. Measurement of changes in the absorption spectra after addition of NBD-Cl to solutions of beta -lactoglobulin A ( beta A) or B ( beta B) in buffers with pH values in the range 4.67-8.2, showed that in borate buffer, pH 8.2, the NBD-Cl reacts with the 2 thiol groups of beta A and beta B. When excess reagent was added, it also reacted with 2 or 3 of the amino groups on the beta A and beta B molecules. Only the reaction with the 2 thiol groups gave rise to a conformational change as deduced from laevorotation increase at 578 nm.