| Property | TAX-4 Homomeric Channel | TAX-2/TAX-4 Heteromeric Channel |
|---|---|---|
| cGMP sensitivity (KD) | High sensitivity; KD ≈ 4 × 10⁻⁷ M for cGMP (pqac-00000000) | ~25-fold lower cGMP sensitivity than TAX-4 alone; still cGMP-gated (pqac-00000000, pqac-00000008) |
| cAMP sensitivity | Poor sensitivity to cAMP; strongly prefers cGMP (pqac-00000000) | Retains selectivity for cGMP over cAMP (pqac-00000000, pqac-00000025) |
| Calcium permeability | Calcium permeable (pqac-00000000) | Highly calcium permeable; supports Ca²⁺ influx in sensory transduction (pqac-00000000, pqac-00000008) |
| Divalent ion block sensitivity | More sensitive to divalent ion block (pqac-00000000) | Less sensitive to divalent ion block than TAX-4 alone (pqac-00000000) |
| Ability to form functional channels independently | Yes; TAX-4 alone can form a functional channel in heterologous expression systems (pqac-00000000, pqac-00000025) | Yes as a co-expressed heteromer; requires both TAX-2 and TAX-4 for this channel composition (pqac-00000000, pqac-00000013) |
| Open time | Longer open time; about 7-fold longer than heteromeric TAX-2/TAX-4 channels (pqac-00000013) | Shorter open time than TAX-4 homomers (pqac-00000013) |
| Structural similarity | CNG channel α-like subunit; channel complex is structurally similar to rod photoreceptor CNG channels (pqac-00000025) | Heteromeric CNG channel most similar to rod photoreceptor channels; TAX-2 is the β-subunit partner (pqac-00000025, pqac-00000000) |


*Table: This table compares the key biophysical features of TAX-4 homomeric channels and TAX-2/TAX-4 heteromeric channels in C. elegans. It is useful for distinguishing the specific functional contribution of TAX-2 as the β-subunit in the sensory CNG channel complex.*