Table 3 Comparisons of CDF Carriers with Crac Channels¹.

   1. Secondary Carriers: catalyze Me²⁺:H⁺ antiport.

Channels: catalyze bidirectional Ca²⁺ flux.

   2. Ubiquitous; in plasma and intracellular membranes of eukaryotes.

Present only in eukaryotes; at the plasma membrane/endoplasmic reticulum junctions.

   3. 6 TMSs; N- and C-termini inside; dimeric.

4 TMSs; N- and C-termini inside; tetrameric.

   4. Much size and sequence divergence.

Little size and sequence divergence.

   5. Two aspartates are critical for Me²⁺ binding.

Two glutamates are critical for Ca²⁺ binding.