A pyridoxal 5′-phosphate protein [3]. The product, 4-aminobutanal, spontaneously cyclizes to form 1-pyrroline, which is a substrate for EC?1.2.1.19, aminobutyraldehyde dehydrogenase. Cadaverine and spermidine can also act as substrates [3]. Forms part of the arginine-catabolism pathway [2].?cf. EC?2.6.1.113, putrescine¡ªpyruvate transaminase.