title: On the reactivities of the tryptophan residues of human alpha-lactalbumin to 2-hydroxy-5-nitrobenzyl bromide.
abstract: The reaction of human alpha-lactalbumin with the tryptophan reagent 2-hydroxy-5-nitrobenzyl bromide has been studied. This protein has 3 tryptophan residues (Trp-60, Trp-104 and Trp-118) all of which are accessible to the reagent at pH 2.7 or 7. Trp-60 of human alpha-lactalbumin is much more reactive than Trp-60 of bovine alpha-lactalbumin (Barman, T. E. (1972) Biochim. Biophys. Acta 257, 297-313). As with bovine alpha-lactalbumin, at pH 2.7, 2-hydroxy-5-nitrobenzyl bromide is specific for tryptophan but at pH 7 His-32 also reacts. When treated with the tryptophan reagent, both alpha-lactalbumins lose their specifier protein activities in the lactose synthase (UDPgalactose:D-glucose 4-beta-galactosyltransferase, EC 2.4.1.22) reaction.
mesh_terms: D015077:2-Hydroxy-5-nitrobenzyl Bromide; D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D006639:Histidine; D006801:Humans; D007768:Lactalbumin / Q000378:metabolism; D007788:Lactose Synthase / Q000378:metabolism; D009596:Nitrophenols; D013329:Structure-Activity Relationship; D014364:Tryptophan
chemical_list: D009596:Nitrophenols; D006639:Histidine; D015077:2-Hydroxy-5-nitrobenzyl Bromide; D014364:Tryptophan; D007768:Lactalbumin; D007788:Lactose Synthase