SPCA, or

Secretory Pathway 440px Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classica ...

Ca²⁺- ATPase, is a

calcium ATPase Ca2+ ATPase is a form of P-ATPase that transfers calcium after a muscle has contracted. The two kinds of calcium ATPase are: *Plasma membrane Ca2+ ATPase (PMCA) *Sarcoplasmic reticulum Ca2+ ATPase (SERCA) Plasma membrane Ca2+ ATPase (PMCA) P ...

-type

P-ATPase The P-type ATPases, also known as E1-E2 ATPases, are a large group of evolutionarily related ion and lipid pumps that are found in bacteria, archaea, and eukaryotes. P-type ATPases are α-helical bundle primary transporters named based upon th ...

encoded for by the genes

ATP2C1 Calcium-transporting ATPase type 2C member 1 is an enzyme that in humans is encoded by the ''ATP2C1'' gene. This gene encodes one of the SPCA proteins, a Ca2+ ion-transporting P-type ATPase The P-type ATPases, also known as E1-E2 ATPases, are a ...

and ATP2C2.

Function

SPCA is found primarily in the membranes of the

golgi apparatus The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles ...

in increasing concentrations from the cis- to the trans-golgi compartments. Following a calcium spike, SPCA proteins are responsible for transporting Ca²⁺ ions from the cytosol to the lumen of the golgi, thus lowering the cytoplasmic concentrations of Ca²⁺ to resting levels. SPCA is also able to transport Mn²⁺ ions into the golgi with high affinity, an ability that the related Ca²⁺-ATPase,

SERCA SERCA, or sarco/endoplasmic reticulum Ca2+-ATPase, or SR Ca2+-ATPase, is a calcium ATPase-type P-ATPase. Its major function is to transport calcium from the cytosol into the sarcoplasmic reticulum. Function SERCA is a P-type ATPase. It reside ...

, does not possess. Since Mn²⁺ ions are not used for signalling like Ca²⁺ ions are, the main reason for transporting them out of the cytosol is to prevent manganese toxicity. The removal of these ions from the cytosol can also be looked upon as supplying the golgi apparatus and thus the entire secretory pathway with these ions. Several proteins within the pathway require either Ca²⁺ ions, Mn²⁺ ions, or divalent ions to function as metal cofactors, such as aminopeptidase P,

Proprotein convertase Proprotein convertases (PPCs) are a family of proteins that activate other proteins. Many proteins are inactive when they are first synthesized, because they contain chains of amino acids that block their activity. Proprotein convertases remove thos ...

s and

sulfotransferase Sulfotransferases (SULTs) are transferase enzymes that catalyze the transfer of a sulfo group from a donor molecule to an acceptor alcohol or amine. The most common sulfo group donor is 3'-phosphoadenosine-5'-phosphosulfate (PAPS). In the case o ...

References

Transmembrane proteins {{transmembranereceptor-stub