1. The oxidation of putrescine in vitro by pig kidney diamine oxidase (EC was increased in the presence of 2-oxosuccinamic acid and malonamic acid. 2. It was inhibited by 3-aminopropionamide, oxaloacetate and pyruvate. 3. 2-Oxosuccinamate was derived from asparagine in virus-transformed baby hamster kidney (BHK) cells growing in tissue culture. 4. Asparagine was decarboxylated more efficiently by transformed than by normal BHK cells. 5. In BHK cells transformed by polyoma virus (Py BHK), 2-oxosuccinamate is the most likely immediate precursor of the 14CO2 arising from [U-14C]asparagine, and there was some evidence for its formation in an asparagine-dependent clone of BHK cells before and after their transformation by hamster sarcoma virus (respectively Asn- and HSV Asn-). 6. The relationship between 2-oxosuccinamate and pyruvate and the possible roles of these two substances in controlling cellular diamine oxidase activity are discussed.

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