TABLE 2.
Amino acid substitutions and kinetic parameters (Ktapp and Vmax) of products of mutated FCY2 allelesa
| FCY2 allele | No. of selected alleles | Amino acid replacement(s) | Transport parameters
|
|||||||
|---|---|---|---|---|---|---|---|---|---|---|
| ADE
|
CYT
|
HYP
|
GUA
|
|||||||
| Ktapp | Vmax | Ktapp | Vmax | Ktapp | Vmax | Ktapp | Vmax | |||
| Wild type | 1.2 | 175 | 2.3 | 240 | 2.5 | 200 | 1.6 | 220 | ||
| paC-A | 6 | S369F | 2.8 | 305 | 26 | 780 | 14 | 115 | 12.5 | 110 |
| paC-B | 1 | T370N | 1.4 | 86 | 18 | 59 | 16.5 | 12 | 9.4 | 11 |
| pcM-A | 31 | N377I | 16 | 248 | 36.5 | 1,750 | 25 | 437 | 28.2 | 99 |
| pcM-B | 10 | N377T | 0.67 | 58 | 9 | 453 | 14.1 | 147 | 20.3 | 57 |
| pcM-C | 7 | G280A | 9.5 | 35 | 13.5 | 380 | 13.2 | 33 | 13.5 | 64 |
| paC-C | 1 | I371V, I375V, N377G, V478A | 2.8 | 250 | 25 | 605 | 23.2 | 65 | 10 | 27 |
| pcM-D | 1 | I371V, I375V, N377G | 3.1 | 288 | 30 | 735 | 17.6 | 48 | 28.8 | 57 |
| pcM-E | 1 | A335S, I371V, I375V, N377G, S441A, F447I | 2.9 | 253 | 27.7 | 495 | 15.8 | 38 | 70 | 107 |
a
paC-type mutated alleles are from CYTr mutants of strain RW123, and pcM-type alleles are from 5MeCr mutants of strain RW126. Ktapp values are apparent Michaelis constants of transport (micromolar). Vmax values are maximal rates of uptake expressed in picomoles of incorporated substrate per 107 cells per minute. Ktapp and Vmax values were determined as described by Brèthes et al. (3), with seven concentrations of radiolabeled substrate. Experiments were performed in duplicate.