[A new fluorogenic substrate of carboxypeptidase H--o-coumaroylphenylalanyl-alanyl-arginine].

New fluorogenic substrate of carboxypeptidase H, Cum-Phe-Ala-Arg-OH, is hydrolyzed by this enzyme to give Cum-Phe-Ala-OH, which is completely extracted by chloroform from the reaction mixture and whose fluorescence increases remarkably by the presence of triethylamine. When the hydrolysis of the novel substrate is compared with Dns-Phe-Ala-Arg-OH, the former has Km twice as low (30 microM) and kcat four times as high (5.8 s-1). Activation of the enzyme by Co2+ in reactions with the two substrates was also studied. The novel substrate is useful for the enzyme's assay in homogenates of various animal tissues.