Selective inhibition of the sperm-specific lactate dehydrogenase isozyme-C4 by N-isopropyl oxamate.
In the present study, we demonstrated that the attachment of the nonpolar isopropylic carbon chain in the nitrogen of oxamate, converted this competitive inhibitor of LDH isozymes into a powerful selective inhibitor of mouse LDH-C4. The comparative study of the inhibitory effect of oxamate and N-isopropyl oxamate on mouse LDH isozymes pointed out that the isopropylic carbon chain conferred upon N-isopropyl oxamate a high affinity for LDH-C4 and a marked decrease in the affinity for the other isozymes since oxamate showed more inhibitory effect on LDH-1 (Ki = 0.06 mM) and LDH-5 (Ki = 0.08 mM), and less inhibitory effect on LDH-C4 (Ki = 0.25 mM). On the other hand, N-isopropyl oxamate showed the highest inhibitory effect on LDH-C4 (Ki = 0.014 mM) and poor inhibitory effect on LDH-1 (Ki = 0.4 mM) and LDH-5 (Ki = 0.8 mM). Apparently, the enzymatic inactivation proceeded through a reversible binding of N-isopropyl oxamate, facilitated by nonpolar interactions with a hydrophobic region present only in the active site of mouse LDH-C4, resulting in a selective inhibition of this isozyme in comparison with the other LDH isozymes. N-isopropyl oxamate was also a powerful competitive inhibitor of LDH-C4 (Ki = 0.015 mM) compared with oxamate (Ki = 0.35 mM), using alpha-ketoisocaproate as a substrate.
Wong
C
C
Departamento de Bioquímica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México DF, Mexico.
Rodríguez-Páez
L
L
Nogueda
B
B
Pérez
A
A
Baeza
I
I
D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase / Q000037:antagonists & inhibitors*; D008297:Male; D051379:Mice; D010072:Oxamic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D013094:Spermatozoa / Q000201:enzymology*; D013379:Substrate Specificity
D004791:Enzyme Inhibitors; D007527:Isoenzymes; C109929:N-isopropyloxamate; D007770:L-Lactate Dehydrogenase; D010072:Oxamic Acid