Table 2.

6MPH₄/BH₄ ratios of rat phenylalanine hydroxylase and the activity after preincubation with phenylalanine

Enzyme	V6MPH4*	VBH4†	Ratio‡	Vphe§	Ratio¶
Wild type	10.9	0.4	27.2	11.1	27.8
N-15	6.5	0.8	8.1	6.3	7.9
N-26	11.4	8.0	1.4	10.9	1.4
N-40	12.0	8.6	1.4	N/A‖	N/A‖
N-59	13.3	10.0	1.3	N/A‖	N/A‖
S29C	6.3	1.5	4.2	6.1	4.1
hR29Cys	6.7	1.9	3.5	8.9	4.7
hR29Ser	10.9	0.7	15.6	11.3	16.1
S29A	7.7	1.5	5.1	7.2	4.8
S29M	6.5	1.8	3.6	6.2	3.4
S29L	6.0	1.7	3.5	6.4	3.8
S29D	6.2	1.5	4.1	6.0	4.0
S29N	6.4	1.4	4.6	6.2	4.4
S29R	8.2	4.3	1.9	7.0	1.6

^*Initial rates were measured with 250 μM 6MPH₄ and 5 mM phenylalanine. 

^† Initial rates were measured with 30 μM BH₄ and 1 mM phenylalanine. 

^‡ 6MPH₄/BH₄ ratio. 

^§ Initial rates for phenylalanine-activated enzymes were determined in the presence of 27 μM BH₄. Enzymes were activated with 1 mM phenylalanine at concentration of 4.0 μM for 5 min at room temperature. Then 10 μl of enzyme was used to determine the initial rate in a reaction volume of 1 ml. 

^¶ V_phe/V_BH4, measurement of the activation by preincubation with phenylalanine. 

^‖ Not available.