TABLE 3.

Specific activity of β-IPM dehydrogenase in lrp⁺ and lrp strains^a

Strainb	lrp allele	Doubling time (min) in medium		Sp. act. of β-IPM dehydrogenaseb
		Without Leu	With Leu	Without Leu	With Leu
P90C	lrp+	57	67	2.0 ± 0.2 (3)	0.2 ± 0.05 (3)
CV1216	lrp-35::Tn10	82	62	1.5 ± 0.03 (3)	0.07 ± 0.03 (3)

^aStrains were grown in minimal glucose medium containing 50 μg (each) of isoleucine, valine, and proline per ml and 5 μg of thiamine per ml in the presence or absence of 100 μg of leucine per ml. Cultures were grown overnight, diluted to an A₅₅₀ of 0.01, and samples were taken at different times in the log phase for assay. 

^bAssays were performed as described previously (19), except that cells were broken by sonication; 2,4-dinitrophenylhydrazones were extracted into toluene and then aqueous sodium carbonate as described by Stieglitz and Calvo (21), except that 1.5 ml of Na₂CO₃ and 0.25 ml of KOH were used and A₅₄₀ was determined. Specific activity is expressed as micromoles per hour per milligram of total protein. Values in parentheses represent the number of samples analyzed. Each sample was assayed in duplicate. A repetition of this experiment gave similar results.