Structure-activity studies of L-canaline-mediated inhibition of porcine alanine aminotransferase.
L-Canaline [L-2-amino-4-(aminooxy)butanoic acid] (L-CAN) and a family of eleven structurally related analogs were synthesized and evaluated for their inhibitory effect on PLP-dependent alanine aminotransferase (AlaAT) (EC 2.6.1.2) obtained from porcine heart. These congeners were selected to determine the stereochemical, aliphatic chain length, and aminooxy substitutional effects on L-CAN-mediated inhibition of AlaAT activity. L-CAN was the most effective inhibitor of the tested compounds; 10(-7) M L-CAN elicited a 55% reduction in AlaAT activity after a 5 min exposure. This deleterious effect results from the ability of L-CAN to react avidly with PLP moiety of the enzyme to form a stable, L-CAN-PLP oxime. In contrast, the methyl and ethyl esters of L-CAN reduced AlaAT activity by only 8% and 6%, respectively. While all of the L-enantiomeric forms of the tested compound were more potent AlaAT inhibitors than their corresponding D-stereoisomers, the D-enantiomers, particularly D-canaline, were active. Chain shortening or lengthening dramatically curtailed L-CAN-mediated loss in AlaAT activity, but the replacement of the alpha-amino group with a hydrogen was of little consequence in this regard. AlaAT was treated with L-CAN in the presence of free PLP to assess PLP capacity to protect AlaAT against 10(7) M L-CAN-dependent inactivation. L-CAN retained approximately two-thirds of its inhibitory ability in the presence of equimolar PLP, but AlaAT inhibition was reduced 90% by a 10-fold excess of PLP over L-CAN.
Worthen
D R
DR
Graduate Center for Toxicology, University of Kentucky, Lexington 40506-0054, USA.
Ratliff
D K
DK
Rosenthal
G A
GA
Trifonov
L
L
Crooks
P A
PA
D000410:Alanine Transaminase / Q000037:antagonists & inhibitors*; D000613:Aminobutyrates / Q000737:chemistry* / Q000494:pharmacology*; D000818:Animals; D009206:Myocardium / Q000201:enzymology; D011732:Pyridoxal Phosphate / Q000737:chemistry; D013329:Structure-Activity Relationship; D013552:Swine
D000613:Aminobutyrates; C001926:canaline; D011732:Pyridoxal Phosphate; D000410:Alanine Transaminase