Inhibition of pyridoxal enzymes by l-canaline

Characterization of ornithine decarboxylase of tobacco cells and tomato ovaries.

“…This non-protein amino acid was shown to inhibit various pyridoxal phosphate-dependent enzymes from animal sources. It was suggested (Rahiala et al, 1971) that the binding of L-canaline to pyridoxal phosphate (free and enzyme-bound) is the cause of the inhibition. Indeed, the L-ornithine decarboxylase derived from tobacco cells is inhibited by L-canaline (Fig.…”

Metabolism of l-Canavanine and l-Canaline in Leguminous Plants

“…Canaline also reacts nonenzymatically to form oximes with pyruvic acid and oxaloacetic acid; these reactions can deplete tricarboxylic acid cycle compounds. Canaline also forms an oxime with pyridoxal phosphate; production of the canaline-pyridoxal phosphate oxime inactivates rapidly vitamin B6-containing enzymes (9,13). Canaline's powerful inhibition of pyridoxal phosphate-containing enzymes, including many decarboxylases and aminotransferases, is documented (9, 13).…”

A Mechanism of l‐Canaline Toxicity

“…The canaline-pyridoxal phosphate complex had mp 174. 5 A Cary model 17 recording spectrophotometer produced the spectral scans. Amino acid analyses were conducted with a Durrum analyzer utilizing their lithium citrate buffer system.…”

“…When canaline is reacted with the holoenzyme, the 387-nm absorption is attenuated while a novel peak at 332 nm makes its appearance (curve 4); these spectral properties are shared by the canaline -pyridoxal phosphate complex. As the canaline concentration increases and its reaction with the native holoenzyme extends further toward completion, the absorbance at 332 nm is steadily enhanced (curves [4][5][6]. From these observations it is reasonable to propose that the diminution in absorbance at 387 nm and generation of the novel response at 332 nm results from the binding of canaline with the B6 moiety of the holoenzyme.…”

“…This contention is predicated upon spectral shifts noted when B6-containing enzymes are treated with canaline [5,6]. While the spectral findings are consistent with the production of such a complex, no direct chemical proof of its existence has been offered.…”