Pathways functional coupling

Organisms Differ in Sources of Energy, Reducing Power, and Starting Materials for Biosynthesis Reactions Are Organized into Sequences or Pathways Sequentially Related Enzymes Are Frequently Clustered Pathways Show Functional Coupling The ATP-ADP System Mediates Conversions in Both Directions... 

The Embden-Mayerhof pathway of glycolysis, also known as anaerobic metabolism, is perhaps an early function coupled directly to photosynthesis, which requires chloroplasts for the recovery of reduction potential from the photolysis of water.15 Chloroplasts were perhaps finished even earlier than any other structure but certainly 3.5 billion years ago lest blue-green algae could not have been blue- green ... 

M Murakami, T Kambe, S Shimbara, I Kudo. Functional coupling between various phospholipase A2s and cyclooxygenases in immediate and delayed prostanoid biosynthetic pathways. J Biol Chem 274 3103-3115, 1999. 

Gu L, Jia J, Liu H, Hakansson K, Gerwick WH, Sherman DH. Metabofic coupling of dehydration and decarboxylation in the curacin A pathway functional identification of a mechanistically diverse enzyme pair. J. Am. Chem. Soc. 2006 128 9014-9015. 

TSH (also called thyrotropin), which is secreted by the pituitary, plays a central role in the regulation of growth and function of the thyroid gland. TSH receptors are functionally coupled to G-proteins thus, the extracellular stimulus by TSH is transduced into intracellular signals mediated by a number of G-proteins. Activation of Gs-protein results in the stimulation of the adenylate cyclase-cAMP-protein phosphorylation cascade. Other G-proteins coupled to TSH-receptor activation include Gg-protein, which mediates the phospholipase C-phosphatidylinositol 4,5-bisphosphate-Ca + signaling pathway (see Chapter 30 for a detailed discussion). 

The folate receptor facilitates the cellular uptake of folate and 5-methyltetrahydrofolate via receptor-mediated endocytosis at caveolae (caveolae are plasma membrane invaginations distinct from the classical clathrin-coated pits) (6). It has been hypothesized that the folate receptor is functionally coupled to an anion transporter to mediate cytosolic folate delivery by a process defined as potocytosis (6). More recent studies suggest that folate receptor endocytosis also occurs at clathrin-coated pits (7). Studies by Low and coworkers at Purdue University have shown that folate conjugates are also taken up by the folate receptor (8-10), but not by the reduced folate carrier. Figure 2 illustrates an endocytic pathway of the type envisioned for folate conjugates. Unfortunately, the subcellular transport pathway of the folate conjugates has been only partially characterized and may well be affected by the properties of the molecule attached to folate. 

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