In higher plants the phytochrome chromophore is a linear tetrapyrrole called phytochromobilin

TLS Online TPP Program

#Id: 9071

#Unit 4. Cell Communication and Cell Signaling

Feedback mechanisms suppress signaling by the PKA pathway:

1. Intrinsic GTPase activity of Gαs

2. PDE acts to hydrolyze cAMP to 5′-AMP

3. By BARK

TLS Online TPP Program

#Id: 9072

#Unit 4. Cell Communication and Cell Signaling

In resting state 

basal level of PDE activity keeps cAMP levels below those necessary for PKA activation.

TLS Online TPP Program

#Id: 9073

#Unit 4. Cell Communication and Cell Signaling

TLS Online TPP Program

#Id: 9074

#Unit 4. Cell Communication and Cell Signaling

Activation of β-adrenergic receptors causes activation of C subunits of PKA which phosphorylate PDE, stimulating its catalytic activity.

TLS Online TPP Program

#Id: 9075

#Unit 4. Cell Communication and Cell Signaling

Active PDE hydrolyzes cAMP, driving cAMP levels back to basal levels.

TLS Online TPP Program

#Id: 9076

#Unit 4. Cell Communication and Cell Signaling

A G protein– coupled receptor kinase phosphorylates serine and threonine residues in the

cytoplasmic segments of activated GPCRs