Figure 4.
A simplified diagram to illustrate 'second messenger' and protein phosphorylation pathways associated with target-cell membrane receptors for three hormones: epinephrine (adrenaline), insulin and prolactin. AC, adenylyl cyclase; cAMP, cyclic AMP; DG, diacylglycerol; Gs and Gi, stimulatory and inhibitory G proteins; IP3, inositide trisphosphate; IRS, insulin receptor substrate; JAK, Janus kinase; PI, phosphatidyl inositol; PK-A and PK-C, phosphokinases A and C; PL-C, phospholipase C; PY, phosphotyrosine; Rα/Rβ, IR and PRLR, receptors for epinephrine, insulin and prolactin, respectively; STAT, signal transduction and transcription factor. The grey squares indicate different protein targets for phosphorylation by different pathways, depending on hormonal signal, species and tissue.