TABLE 3.

Kinetic parameters of inhibition

K_i for the penems was determined by measuring initial steady-state velocities in the presence of a constant concentration of enzyme with increasing concentrations of inhibitors against nitrocefin (100 μm); the value was then corrected for nitrocefin affinity. IC₅₀ was determined by measurements of inhibitor concentration that reduces the initial velocities by 50% after 5-min preincubation of enzyme with inhibitor. t_n was determined as the ratio of inhibitor concentration to enzyme concentration necessary to decrease enzyme activity by 95% after 24 h.

Inhibitors	Enzymes
	OXA-1			OXA-24
	Ki	IC50	tn	Ki	IC50	tn
	nm	nm		nm	nm
Penem 1	50 ± 8	30 ± 8	2	30 ± 2	150 ± 30	900
Penem 3	380 ± 70	60 ± 5	2	150 ± 20	160 ± 40	925