Gi alpha subunit

Gi alpha subunit (or Gi/G0 or Gi protein) is a heterotrimeric G protein subunit which inhibits the production of cAMP from ATP.

Receptors
The following G-protein coupled receptors couple to the Gi subunit:
 * 5-HT receptor type 1
 * Adenosine receptor A1 and A3
 * Prostaglandins

Function
Further reading: function of cAMP-dependent protein kinase

Gi inhibits the production of cAMP from ATP, which, in turn, results in decreased activity of cAMP-dependent protein kinase. Thus, the ultimate effect of Gi is thus the opposite of cAMP-dependent protein kinase, which can be found at function of cAMP-dependent protein kinase.

Types
There are several types of Gi: Gia1, Gia2, Gia3 and Gia4

Gia1
Gia1 or Gi1 is encoded by the gene GNAI1.

Gia2
Gia2 or Gi2 is encoded by the gene GNAI2.

Gia3
Gia3 or Gi3 is encoded by the gene GNAI3.