Proposed pathway for agmatine catabolism in A. niger. The different enzymatic steps are numbered as follows: 1, agmatine oxidase; 2, GBald/GABald dehydrogenase; 3, GBase; 4, GABA transaminase; 5, SSA dehydrogenase; 6, GBald ureohydrolase. Likely steps and metabolites in the alternate path for GBald are in gray.