(3-lactamase extracted from two highly (3-lactam resistant isolates of Pseudomonas aeruginosa was purified and characterized. The results of the purification steps indicate that the /3-lactamase from P. aeruginosa Z 90 was purified at 44.6 fold, the specific activity reached to 18.28 units/mgprotein and the yield percentage was reached 50.15 %, while the (3-lactamase from P.aeruginosa Z 33 was purified at 42.4 fold, the specific activity reached to 20.8 units/mg protein and the yield percentage was reached to 61.66 %. With respect to its optimum pH, the optimum values for (3-lactamase from P.aeruginosa Z 33 and P.aeruginosa Z 90 were 7.5 and 8.0, respectively. The optimum temperature
was around 40°C for both enzymes from the two isolates. Studying the heat stability of (3-lactamase revealed that the enzyme of P.aeruginosa Z90 was more stable than the enzyme from P.aeruginosa Z 33. The enzyme activity was increased linearly with increasing (3-lactamase concentration with small deviation of linearity at higher concentrations in the two isolates. Amino acid analysis of the purified (3-lactamase from the two isolates indicate that alanine was the most abundant amino acid in the two isolates. Isolucine was the least detected amino acid in (3-lactamase from P.aeruginosa Z 90 with a percent of 3.12 % while tyrosine was the least one in P. aeruginosa Z 33 with a per cent of 1.93 %. The results of inhibition profiles show that (3-lactamase from the two isolates was strongly inhibited by 0.1 mM CuSO^ but not by EDTA. (3-lactam
inhibitors results indicated that carbenicillin was the stronger inhibitor for the purified (3-lactamase from P.aeruginosa Z 33, while amoxycillin was the stronger one for the enzyme from P.aeruginosa Z 90.