Pathway: The proton buffering model
Reactions in pathway: The proton buffering model :
The proton buffering model
The "proton buffering" model proposes that UCP1 is intrinsically a proton carrier, and that fatty acid acts as a prosthetic group during proton transport. Fatty acid penetrates from the lipid phase, with its carboxyl group oriented to the proton translocation path. Here, it works as a donor-acceptor of protons between the residual carboxyl groups of UCP1. Ultimately, protons are extruded to the matrix side of the membrane.
Rial et al (2004) suggest fatty acids are inducers of proton transport by UCP by allowing themselves to become substrates for UCP and activation of the proton buffering mechanism itself. Binding of nucleotides to UCP inhibits it's proton transport capability. UCP accepts purine ribose tri- and di- nucleotides; GTP, ATP, GDP and ADP. The monophosphates GMP and AMP are poor ligands for UCP binding.
Rial et al (2004) suggest fatty acids are inducers of proton transport by UCP by allowing themselves to become substrates for UCP and activation of the proton buffering mechanism itself. Binding of nucleotides to UCP inhibits it's proton transport capability. UCP accepts purine ribose tri- and di- nucleotides; GTP, ATP, GDP and ADP. The monophosphates GMP and AMP are poor ligands for UCP binding.
The metabolism of pyruvate provides one source of acetyl-CoA which enters the citric acid (TCA, tricarboxylic acid) cycle to generate energy and the reducing equivalent NADH. These reducing equivalents are re-oxidized back to NAD+ in the electron transport chain (ETC), coupling this process with the export of protons across the inner mitochondrial membrane. The chemiosmotic gradient created is used to drive ATP synthesis.
Metabolic processes in human cells generate energy through the oxidation of molecules consumed in the diet and mediate the synthesis of diverse essential molecules not taken in the diet as well as the inactivation and elimination of toxic ones generated endogenously or present in the extracellular environment. The processes of energy metabolism can be classified into two groups according to whether they involve carbohydrate-derived or lipid-derived molecules, and within each group it is useful to distinguish processes that mediate the breakdown and oxidation of these molecules to yield energy from ones that mediate their synthesis and storage as internal energy reserves. Synthetic reactions are conveniently grouped by the chemical nature of the end products, such as nucleotides, amino acids and related molecules, and porphyrins. Detoxification reactions (biological oxidations) are likewise conveniently classified by the chemical nature of the toxin.
At the same time, all of these processes are tightly integrated. Intermediates in reactions of energy generation are starting materials for biosyntheses of amino acids and other compounds, broad-specificity oxidoreductase enzymes can be involved in both detoxification reactions and biosyntheses, and hormone-mediated signaling processes function to coordinate the operation of energy-generating and energy-storing reactions and to couple these to other biosynthetic processes.