Bimane fluorescent labels. Characterization of the bimane labeling of human hemoglobin

The products of the bimane labeling (using a monobromobimane, a dibromobimane and a quaternary bromobimane) of hemoglobin are characterized. Peptide mapping identifies cysteine-beta 93 as the reactive thiol site. Electrophoretic mobility of hemoglobin varies with the label used, that of monobromobimane-labeled hemoglobin being unaltered, while dibromobimane- and trimethylammoniobromobimane-labeled hemoglobin exhibit changes. The oxygen affinity of labeled hemoglobin is changed from that of hemoglobin. Deoxyhemoglobin is substantially less reactive towards monobromobimane than oxyhemoglobin. Bimane-labeled hemoglobin is more easily denatured on heating than unlabeled hemoglobin. Possible uses for bimane labels in the study of protein properties are pointed out. Bimane labeling agents are derivatives of 3,4,6,7-tetramethyl-1,5-diazabicyclo[3.3.0]-octa-3,6-diene-2,8-dione 9,10-dioxa-syn-(methyl,methyl)bimane).