TABLE 1

Kinetic parameters for triazolam metabolism by liver and intestinal microsomes

All the values are the means of three independent experiments ± S.D. Incubations were performed as described under Materials and Methods. Note that mouse intestinal microsomes were isolated from the whole tissue, whereas the human intestinal microsomes were isolated after enterocyte isolation and are enriched in P450.

Microsome, Strain	1′-OH Triazolam			4-OH Triazolam
Microsome, Strain	K_m	V_max	V_max/K_m	K_m	V_max	V_max/K_m
	μM	pmol/min/mg protein	μl/min/mg protein	μM	pmol/min/mg protein	μl/min/mg protein
Liver
Wild-type	11.7 ± 1.96	742 ± 16.4	63.5	124 ± 12.9	956 ± 75.1	7.74
Cyp3a(−/−)	73.3 ± 18.8^{^a}	115 ± 14.2^{^a}	1.56	53.1 ± 1.32	27.6 ± 1.05	0.52
Cyp3a(−/−)Tg-3A4_Hep	58.4 ± 8.46	2145 ± 124	36.8	406 ± 80.0	6485 ± 907	16.0
Cyp3a(−/−)Tg-3A4_Int	40.1 ± 2.73^{^a}	56.5 ± 3.14^{^a}	1.41	72.9 ± 8.22	18.0 ± 0.99	0.25
Human	37.2 ± 3.27	1156 ± 42.2	31.1	168 ± 26.1	2070 ± 124	12.3
Intestine
Wild-type	^{^b}	^{^b}		^{^b}	^{^b}
Cyp3a(−/−)	^{^c}	^{^c}		^{^c}	^{^c}
Cyp3a(−/−)Tg-3A4_Hep	^{^c}	^{^c}		^{^c}	^{^c}
Cyp3a(−/−)Tg-3A4_Int	38.5 ± 4.04	194 ± 5.87	5.05	510 ± 27.6	894 ± 28.7	1.75
Human	53.7 ± 3.01	847 ± 19.6	15.8	345 ± 40.8	2439 ± 215	7.07

↵a Fitted with substrate inhibition model as described under Materials and Methods.
↵b Metabolite observed but kinetics could not be assessed.
↵c No metabolite detected (<2.5 pmol/min/mg protein).