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====Ortak yol====
[[Image:GPCR-Zyklus.png|thumb|300px|G-protein eşlenik almaç ile aktivasyon döngüsü]]
Almaçla aktiflenen G proteinleri [[hücre zarı]]nın iç yüzeyinde bulunurlar.G<sub>α</sub> ve G<sub>βγ</sub> altbirimleri içerirler.G<sub>α</sub> altbiriminin pek çok alt birimi vardır:G<sub>s</sub>α (G stimulan), G<sub>i</sub>α (G inhibitör), G<sub>o</sub>α (G diğer), G<sub>q/11</sub>α, ve G<sub>12/13</sub>α gibi.Aynı aktivasyon mekanizmasını kullanarak farklı effektörlere etki ederler.
There are many classes of G<sub>α</sub> subunits: G<sub>s</sub>α (G stimulatory), G<sub>i</sub>α (G inhibitory), G<sub>o</sub>α (G other), G<sub>q/11</sub>α, and G<sub>12/13</sub>α are some examples. They behave differently in the recognition of the effector, but share a similar mechanism of activation.
=====Aktivasyon=====
Bir ligand [[G protein eşlenik almaç]]ları aktiflediğinde, reseptörde konformasyonel bir değişiklik oluşturarak onu bir [[GEF]] yani guanin exchange faktörü haline getirir
When a [[ligand]] activates the [[G protein-coupled receptor]], it induces a conformational change in the receptor that allows the receptor to function as a [[guanine nucleotide exchange factor]] ([[GEF]]) that exchanges GDP for GTP on the G<sub>α</sub> subunit. In the traditional view of heterotrimeric protein activation, this exchange triggers the dissociation of the G<sub>α</sub> subunit, bound to GTP, from the G<sub>βγ</sub> dimer and the receptor. However, models that suggest molecular rearrangement, reorganization, and pre-complexing of effector molecules are beginning to be accepted.<ref name="pmid17095603">{{cite journal | author = Digby GJ, Lober RM, Sethi PR, Lambert NA. | title = Some G protein heterotrimers physically dissociate in living cells.| journal = Proc Natl Acad Sci USA |pmid = 17095603. | year = 2006 | volume = 103 | issue = 47 | pages = 17789–94 | doi = 10.1073/pnas.0607116103 | pmc = 1693825}}</ref><ref name="pmid19089952">{{cite journal | author = Khafizov K, Lattanzi G, Carloni P | title = G protein inactive and active forms investigated by simulation methods| journal = PROTEINS : Structure, Function, and Bioinformatics |pmid = 19089952. | year = 2009 | volume = 75 | issue = 4 | pages = 919–30 | doi = 10.1002/prot.22303}}</ref> Both G<sub>α</sub>-GTP and G<sub>βγ</sub> can then activate different ''signaling cascades'' (or ''second messenger pathways'') and effector proteins, while the receptor is able to activate the next G protein.<ref>{{cite journal | author = Yuen, Jessie W.F. | title = Activation of STAT3 by specific G[alpha] subunits and multiple G[beta][gamma] dimers | journal = The International Journal of Biochemistry & Cell Biology | volume = 42 | number = 6 | pages = 1052–1059 | year = 2010 | issn = 1357-2725 | doi = DOI: 10.1016/j.biocel.2010.03.017}}</ref>
=====Terminasyon=====
The G<sub>α</sub> subunit will eventually [[Hydrolysis|hydrolyze]] the attached GTP to GDP by its inherent [[enzyme|enzymatic]] activity, allowing it to re-associate with G<sub>βγ</sub> and starting a new cycle. A group of proteins called [[Regulator of G protein signalling]] (RGSs), act as [[GTPase-activating proteins]] (GAPs), specific for G<sub>α</sub> subunits. These proteins act to accelerate hydrolysis of GTP to GDP and terminate the transduced signal. In some cases, the effector itself may possess intrinsic GAP activity, which helps deactivate the pathway. This is true in the case of [[phospholipase C]] beta, which possesses GAP activity within its C-terminal region. This is an alternate form of regulation for the G<sub>α</sub> subunit.
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