TABLE 2.

Substrate profiles of β-lactamases recovered directly from M. tuberculosis and recombinant Y49 β-lactamase

Substratea	Relative rate of hydrolysisb
	Peak 1c	Peak 2c	Peak 3c	Recombinant Y49 β-lactamased
Benzylpenicillin	100	100	100	100
Azlocillin	234	200	91	153
Nitrocefin	78	82	216	84
Cephaloridine	5	9	55	8
Cefazolin	4	4	85	5

^aThe substrate concentrations used in these determinations were 500 μM for the penicillins and 100 μM for the cephalosporins. 

^bThe initial velocity of hydrolysis of benzylpenicillin was fixed at 100, and the relative rate of hydrolysis of other substrates has been expressed as a percentage of the value for benzylpenicillin. 

^cPeak 1, peak 2, and peak 3 refer to the partially purified enzyme in β-lactamase-containing fractions recovered directly from M. tuberculosis H37Ra by chromatofocusing (Fig. 2). 

^dRecombinant Y49 β-lactamase refers to the purified recombinant β-lactamase, expressed in E. coli, which corresponds to the β-lactamase gene encoded on cosmid Y49.