Ryanodine receptor protein (RYR)
The ryanodine receptor (RYR) functions as a channel for release of
calcium from endoplasmic reticulum of muscle and brain. The isoforms
are ~5000 residues long and contain two EF- hands, the second of which
is inferred to bind calcium. The channels open in the presence of
~10-6 M Ca2+ (calcium induced calcium release) and closed at ~10-3 M
Ca2+. The EF-hands have low calcium affinity and have been suggested
to function in closing the channels .