. Author manuscript; available in PMC: 2020 Dec 1.

Published in final edited form as: Biochem Pharmacol. 2019 Oct 9;170:113661. doi: 10.1016/j.bcp.2019.113661

Table 1.

Michaelis-Menten kinetic constants for terbinafine N-dealkylation pathways.^a

P450 isozyme	Pathway	Step	Substrate	Steady-state kinetic constants for individual metabolites
P450 isozyme	Pathway	Step	Substrate	V_max^b	K_m (μM)	V_max/K_m	V_max^b	K_m (μM)	V_max/K_m
CYP1A2^d	Pathway 1	1	terbinafine	TBF-A^c			N-methyl-1-naphthyl-methylamine
	Pathway 1	1	terbinafine	-	75 ± 42	-	100 ± 12	31 ± 17	3.2
	Pathway 2	2.1	terbinafine	formaldehyde			desmethyl-terbinafine
	Pathway 2	2.1	terbinafine	high background masked rates			530 ± 38	120 ± 23	4.4
CYP2B6^e	Pathway 1	1	terbinafine	TBF-A			N-methyl-1-naphthyl-methylamine
	Pathway 1	1	terbinafine	undetected			1300 ± 280	470 ± 170	2.8
	Pathway 2	2.1	terbinafine	formaldehyde			desmethyl-terbinafine
	Pathway 2	2.1	terbinafine	high background masked rates			1200± 150	220 ± 64	4.8
		2.2a	desmethyl-terbinafine	TBF-A^c			1-naphthyl-methylamine
		2.2a	desmethyl-terbinafine	-	495	-		linear	4.8^f
		2.2b	desmethyl-terbinafine	1-naphthaldehyde^g			6,6-dimethyl-2-hepten-4-yn-1-amine
		2.2b	desmethyl-terbinafine	9100 ± 6200	2700 ± 2100	3.4	undetected
CYP2C8^e	Pathway 2	2.1	terbinafine	formaldehyde			desmethyl-terbinafine
	Pathway 2	2.1	terbinafine	high background masked rates			260 ± 12	72 ± 12	3.6
		2.2a	desmethyl-terbinafine	TBF-A^c			1-naphthyl-methylamine
		2.2a	desmethyl-terbinafine	-	133	-	85 ± 6.5	98 ± 23	0.87
		2.2b	desmethyl-terbinafine	1-naphthaldehyde			6,6-dimethyl-2-hepten-4-yn-1-amine
		2.2b	desmethyl-terbinafine	300 ± 28	110 ± 28	2.9	undetected
CYP2C9^e	Pathway 1	1	terbinafine	TBF-A^c			N-methyl-1-naphthyl-methylamine
	Pathway 1	1	terbinafine	-	35 ± 5.0	-	800 ± 170	380 ± 150	2.1
	Pathway 2	2.1	terbinafine	formaldehyde			desmethyl-terbinafine
	Pathway 2	2.1	terbinafine	high background masked rates			400 ± 19	20 ± 5.1	20
		2.2a	desmethyl-terbinafine	TBF-A^c			1-naphthyl-methylamine
		2.2a		-	235	-	330 ± 41	380 ± 88	0.87
		2.2b	desmethyl-terbinafine	1-naphthaldehyde			6,6-dimethyl-2-hepten-4-yn-1-amine
		2.2b	desmethyl-terbinafine	69 ± 4.4	140 ± 26	0.49	undetected
CYP2D6^d	Pathway 1	1	terbinafine	TBF-A			N-methyl-1-naphthyl-methylamine
	Pathway 1	1	terbinafine	undetected			450 ± 74	200 ± 75	2.3
	Pathway 2	2.1	terbinafine	formaldehyde			desmethyl-terbinafine
	Pathway 2	2.1	terbinafine	high background masked rates			190 ± 32	45 ± 19	4.2

Data fit best to the Michaelis-Menten equation over the Hill equation (P < 0.05) shown in Fig 2. Values shown with standard deviation from mean. Limit of quantitation calculated as standard deviation of response divided by slope of standard curve, whether metabolite was labeled or not. Pathway step 3.2 was not studied due to absence of authentic standards and low efficiency of previous step to obviate the significance of this pathway for TBF-A.

Units are pmol/min/nmol protein.

V_max values highly variable so efficiency values could not be reliably calculated.

There were no detectable metabolites for Pathway Steps 1.2, 2.2a, 2.2b, or 3.

There were no detectable metabolites for Pathway Steps 1.2 or 3.

Efficiency expressed as slope of formation rate over substrate concentration due to lack of observed saturation.

Non-linear kinetic profile but poor fit to Michaelis-Menten equation due to inability to saturate enzyme, and thus reported kinetics are not highly reliable.