Characterization of slow reacting substances (SRSs) of rat basophilic leukemia (RBL-1) cells: effect of cysteine on SRS profile.

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Abstract
When RBL-1 [rat basophilic leukemia] cells were incubated with L-cysteine (7.5 mM) and the ionophore A23187, the slow reacting substances SRS-GSH [5-hydroxy-6-.gamma.-glutamylcysteinylglycyl-7,9,11,14-eicosatetraenoic acid] and SRS-Cys-Gly [5-hydroxy-6-.gamma.-cysteinylglycyl-7,9,11,14-eicosatetraenoic acid] were formed. When L-cysteine was omitted in the incubation, SRS-GSH and SRS-Cys [5-hydroxy-6-S-cysteinyl-7,9,11,14-eicosatetraen acid] were isolated but only a trace amount of SRS-Cys-Gly was detectable. Each of the characterized SRS was accompanied by an as yet uncharacterized structural isomer showing UV absorption at 278 nm. L-Cysteine and other thiols inhibited an aminopeptidase that transforms the highly bioactive SRS of anaphylaxis (SRS-Cys-Gly) into the less bioactive SRS-Cys. SRS-GSH, SRS-Cys-Gly and SRS-Cys may be readily distinguished from each other by means of their bioactivities, antagonism by FPL 55712 [7-[3-(4-acetyl-3-hydroxy-2-propylphenoxy)-2-hydroxypropoxy]-4-oxo-8-propyl-4H-1-benzopyran-2-carboxylic acid monosodium salt] and relative susceptibilities to the actions of soybean lipoxygenase, microsome-bound leucine aminopeptidase and .gamma.-glutamyl transpeptidase.