FiFoATPases

Thee FiFo-ATPase is a splendid molecular machine. (P. Boyer) F1Fo-ATPases (or F-type ATPases for short) are found in the plasma membrane of bacteria and in the organelles derived from them (mitochondria and plastids). They act as ATP-synthases, using the chemosmotic energy of a proton gradient across the membrane to drive ATP-synthesis (Mitchell-hypothesis, NoBEL-Price 1978). Remember that reactions are always written in the direction of negative AG0, thus ATP is the substrate and ADP + P are...

Use of enzymes for diagnostics

Many enzymes occur only in certain specialised cells in our body. If those cells are damaged, enzyme molecules are released into the circulation. Thus determination of enzyme activities is an important diagnostic tool in the clinical laboratory. For example creatine kinase (CK) is prevalent in muscle cells. Destruction of heart muscle cells in an acute myocardial infarct or of skeletal muscle cells in DuCHENNE muscular dystrophy leads to the appearance of CK in the blood. Interestingly,...

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Enzymatic conversion of substrate to product enzymatic conversion of substrate to product Figure 6.6. Increase of P over time in an enzymatic reaction. The reaction velocity ( dtr) is highest at the t 0, it approaches zero as the ratio of P S approaches the equilibrium. The reaction velocity at t 0 is called initial velocity. Figure 6.6. Increase of P over time in an enzymatic reaction. The reaction velocity ( dtr) is highest at the t 0, it approaches zero as the ratio of P S approaches the...

Catalytic perfection and multienzyme complexes

The rate limiting step in an enzymes reaction can be either the association of enzyme with its substrate, or the conversion to and release of product. The association velocity is described by the association rate constant k+i, which is in the order of 1 x 109 s_1. This is the rate at which substrate can diffuse and bind to the enzyme in a dilute, aqueous medium at physiological temperatures. If the efficiency constant is of the same order of magnitude (note that it has the same unit ) the...

Sesep E P62

Because the conversion of ES to EP does not involve binding or release steps, its speed is independent of the concentration of reactants. Thus we can further simplify If the conversion of ES to E + P is much slower than the binding of S to E (rapid equilibrium assumption), the reaction velocity (rate of product formation or substrate consumption) will be proportional to the concentration of ES By the law of mass action, the concentration of ES depends on the concentration of E and S

A6 Acronyms

ABC ATP binding cassette, major family of primary active transporters AE1 anion exchanger 1, also called band-3 protein, equilibrates chloride and bicarbonate across the erythrocyte membrane AIDS acquired immune deficiency syndrome, life-threatening sexually transmitted disease caused by HIV AMP-PCP adenosine 5' , 7-methylene triphosphate, non-hydrolysable ATP-derivate, the oxygen between the - and 7-phosphate is replaced by an methylene (-CH2-) group. AMP-PNP adenosine 5' , 7-imino...

U Ii U U

Ion exchange affinity, HIC gel filtration ion exchange affinity, HIC gel filtration Figure 3.1. Principles of chromatography. The sample is moved by a solvent (mobile phase) past a matrix (stationary phase). Different sample molecules have different partition coefficients between mobile and stationary phase and are delayed differently. Separation can be by ionic interactions, specific interactions with a ligand and size exclusion. For details see text. - The electrical charge of proteins...

Inhibition of Enzymes

The usual view of enzymes (and receptors) is that they bind very specifically their substrates, but nothing else. If this were the case it would be impossible to influence disease with pharmaceuticals, because most of them work by binding to enzymes and receptors and blocking their action. Binding can be reversible or irreversible reversible binding results in inhibition, irreversible binding in inactivation of the enzyme or receptor (the latter will be dealt with in the next section)....

Crystal structure and reaction mechanism of LacY

Of the MFS-proteins currently only one example structure at molecular resolution (3.6 A) is available 1 , that of the E. coli lactose permease (LacY, see fig. 17.11). The molecule consists of two domains (helices 16 and 7-12), which are folding homologues although sequence homology is low. A mutant protein (C154G) was used for crystallisation, as this mutant is locked in the inward-facing conformation. This reduction in conformational freedom makes crystallisation possible, at the resolution of...

Enzyme kinetics special cases

In an enzyme following HMM-kinetics, enzyme activity rises gradually with substrate concentrations. For many physiological situations this is appropriate, the enzyme activity adapts to the metabolic needs of the cell. In this chapter we want to look at some cases, where such a gradual response would be inadequate, where instead a steep, switch-like, all-or-nothing response is required. Binding of a few hormone molecules to the receptors on the membrane of a cell can affect considerable changes...

Inherited diseases relating to haemoglobin

Sickle cell anaemia is an autosomal recessive disorder (i.e. the gene needs to be inherited from both parents for the disease to become manifest) which affects mostly Africans and their descendants. It is caused by a mutation in the gene for the ,3-subunit of haemoglobin (pS), leading to the substitution of Glu-6 with Val. The resulting haemoglobin is called HbS. The substitution of a charged amino acid by a hydrophobic one creates a hydrophobic patch, which is exposed in deoxy-haemoglobin, but...

Uncoating of clathrin coated vesicles

Uncoating Clathrin Coated Vesicles

Because of their clathrin coats, clathrin coated vesicles can not fuse directly with the endosome. And because clathrin coats form spontaneously, energy is required to disassemble them again. This reaction is catalysed by a molecular chaperone, Hsc70 (see page 212), also known as the uncoating ATPase. There is an equilibrium between bound and free clathrin arms. Hsc70-ATP binds to exposed clathrin arms, preventing them from rejoining the coat. This shifts the equilibrium from coat assembly to...

A2 Short biographies of scientists mentioned in this book

Alper, Tikvah South Africa, 1909-1995. Born as fourth daughter of an immigrant from Russia she obtained a scholarship to study Physics at Capetown University, where she received her M.A. at the age of 20. She then moved to Germany, where she worked on the -rays from a-particles with L. Meitner but failed to obtain a PhD because growing antisemitism in Germany forced her to return to South Africa (she was awarded a D.Sc. by London University in 1969). She married the bacteriologist Max Stern in...

A brief history of enzymology

Most of the topics in this brief overview are covered in more detail in the following chapters. For further reading into enzymology 5, 18, 45 are suggested. If you have to deal with rate equations in special cases 70 is still useful. The properties of catalysts were described by the German-Russian chemist Gottlieb Sigismund Constantin Kirchhoff, who could show in 1812 that the hydrolysis of starch to glucose is accelerated by acid, and that the acid is not used up in the process1. In 1814 he...

Shuttles uniporters

Shuttles bind their substrates on one side of the membrane and release it on the other. The simplest shuttles are the so called uncouplers, lipophilic acids that dissolve in the membrane of mitochondria, bind protons on the acidic side and release them on the basic. Thus the proton gradient across the mitochondrial membrane is dissipated (the stored energy is converted into heat) and ATP production ceases. Figure 17.12. 2,4-Dinitrophenol is a typical uncoupler. The hydrophobic molecule can...

L

Immunoglobulin Nature

Antibodies consist of several copies of a characteristic motive, two anti-parallel -pleated sheets on top of each other and connected by a disulphide bond (see fig. 10.2). This Ig-fold is found in many proteins in the immune system and some other proteins with different function. There are some differences in the sequences even of the constant regions of antibodies between individuals. About 20 such allotypes have been identified in human heavy, a few more in the light chain. Some such...

C5

Classical pathway of complement activation. Top The C1q,r,s complex can bind to immunoglobulins bound to antigen. At least 1 IgM or 2 IgG are required. Binding of the hexameric C1q protein to Ig results in C1r cleaving and activating C1s. Activated C1s can cleave C4 into C4a a weak inflammatory peptide and C4b, which binds to the membrane. This binding is covalent Cleavage of C4 exposes a reactive thioester bond between Glu and Cys in C4b, which reacts with OH-groups in proteins...

Cytogenetics

Colchicine from the autumn crocus Colchicium autumnale L., an alpine flower is used to treat acute gout, but can also arrest cells in metaphase by tubulin-depolymerisation. Metaphase-cells have their chromosomes fully condensed and aligned at the equatorial plate of the cell. Thus white blood cells or amniotic cells, stimulated into mitosis by phytohaemagglutinin and Figure 12.8. The autumn crocus Colchicium autumnale L., top left produces colchicine top right , a substance that can...

Immunoproteins

If you wish for peace, prepare for war. Latin proverb The human body is a nutrient rich environment and would be colonised rapidly by viruses, bacteria and other parasites if it were not protected by an immune system. This system not only recognises and destroys invading parasites and even cancer cells , but does not attack the bodies own cells. Both properties are equally important for our survival. An attack of our immune system against our own cells is called autoimmune disease. Such...