L-Canaline is a well-known irreversible inhibitor of ornithine aminotransferase (OAT). The natural L-enantiomer reacts by oxime formation with pyridoxal 5′-phosphate in the active site of the enzyme [1]. L-Canaline is naturally found in plants such as legumes, and has been involved in the metabolism of L-canavanine, an aminooxy analog of arginine [2].
Ornithine aminotransferase (OAT) is a mitochondrial enzyme involved in catalyzing the interaction of L-ornithine and α-ketoglutarate to produce glutamic-y-semialdehyde and glutamate [3].
In vitro: Canaline strongly inhibited the activity of pyridoxal-dependent enzymes, including amino acid decarboxylases, 5-hydroxytryptophan decarboxylase, aminotransferases, tyrosine aminotransferase, ornithine transcarbamylase and plasma diamino-oxidase. The canaline inhibition was due to complex formation between canaline and the pyridoxal coenzyme. l-canaline is one of the most potent inhibitors of pyridoxal enzymes. The IC50 value of l-canaline against Ornithine aminotransferase was 3 ×10-6M [4].
In vivo: Intraperitoneal administration of 500 mg of DL-canaline/kg body wt. only produced a transient inhibition of OAT in brain and liver by 65-70%, suggesting that DL-canaline was not a useful tool in studies of biological consequences of OAT inhibition. [1].
References:
[1] Bolkenius F N, Kndgen B, Seiler N. DL-canaline and 5-fluoromethylornithine. Comparison of two inactivators of ornithine aminotransferase[J]. Biochemical Journal, 1990, 268(2): 409-414.
[2] Rosenthal G A, Rhodes D. L-Canavanine transport and utilization in developing jack bean, Canavalia ensiformis (L.) DC.[Leguminosae][J]. Plant physiology, 1984, 76(2): 541-544.
[3] Peraino C, Bunville L G, Tahmisian T N. Chemical, physical, and morphological properties of ornithine aminotransferase from rat liver[J]. Journal of Biological Chemistry, 1969, 244(9): 2241-2249.
[4] Rahiala E L, Kekomki M, Jnne J, et al. Inhibition of pyridoxal enzymes by L-canaline[J]. Biochimica et Biophysica Acta (BBA)-Enzymology, 1971, 227(2): 337-343.