Feline Congenital Erythropoietic Porphyria: Two Homozygous UROS Missense Mutations Cause the Enzyme Deficiency and Porphyrin Accumulation

Table 4 Prokaryotic expression and characterization of the purified wild-type and mutant URO-synthase enzymes of the CEP cat.

cDNA mutation	Predicted protein	Specific activity, % of WT (n)^a	Total purified expressed enzyme protein,^b % of WT	Thermolability at 50°C^c
cDNA mutation	Predicted protein	Specific activity, % of WT (n)^a	Total purified expressed enzyme protein,^b % of WT	T_1/2 (n) (min)^d	% of Initial at 15 min, %^e
WT	None	100 (8)	100	9.0 (4)	28
c.140C>T	p.S47F	100 (5)	59	4.8 (2)	11
c.331G>A	p.G111S	59 (4)	10	1.3 (2)	0.1
c.140C>T/c.331G>A	p.S47F/p.G111S	19 (7)	2	1.6 (2)	0.3

^a100% = 571,000 nmoles/h/mg protein.
^b100% = 35.3 mg/L of expression culture; n = 1.
^c50°C, pH, 7.4.
^dThe results at time = 15 min were calculated from the linear semilog plots from which the T_1/2 values were determined.
^ePercent of initial enzyme activity.

ISSN: 1528-3658