Special proteins

An enzyme is a special protein that acts as a catalyst for biochemical reactions. 

Intermediates in fatty acid synthesis are linked covalently to the suifhydryl groups of special proteins, the acyl carrier proteins. In contrast, fatty acid breakdown intermediates are bound to the —SH group of coenzyme A. Fatty acid synthesis occurs in the cytosol, whereas fatty acid degradation takes place in mitochondria. 

The major components of the ECM are the structural proteins collagen, elastin, and fibrihin a number of specialized proteins (eg, fibronectin and laminin) and various proteoglycans. 

A biochemical catalyst is called an enzyme. Enzymes are specialized proteins that catalyze specific biochemical reactions. Some enzymes are found in extracellular fluids such as saliva and gastric juices, but most are found inside cells. Each type of cell has a different array of enzymes that act together to determine what role the cell plays in the overall biochemistry of the organism. Enzymes are complicated molecules. Biochemists have determined the molecular structures of some enzymes, but the structures of many enzymes are not yet known. 

The pathway of the metabolic process converting the original nutrients, which are of rather complex composition, to the simple end products of COj and HjO is long and complicated and consists of a large number of intermediate steps. Many of them are associated with electron and proton (or hydrogen-atom) transfer from the reduced species of one redox system to the oxidized species of another redox system. These steps as a rule occur, not homogeneously (in the cytoplasm or intercellular solution) but at the surfaces of special protein molecules, the enzymes, which are built into the intracellular membranes. Enzymes function as specific catalysts for given steps. 

SWISS-PROT, which can be classified as a computer-annotated sequence repository. The issues of completeness and redundancy are also described, and examples of specialized protein sequence collections are given. 

There are many specialized protein sequence databases. Some of them are quite small and contain only a handful of entries others are wider in scope and larger in size. This section describes three examples of specialized protein sequence databases. As this category of databases is quite changeable, any list provided here would soon be outdated. However, under the URL http //www.expasy.ch/alinks.html Proteins is a www document that lists information sources for molecular biologists that is continually update. 

Since all seawater is undersaturated with respect to BSi, plankton that deposit siliceous hard parts must fight unfevorable thermodynamics. In the case of the diatoms, the phytoplankton have specialized proteins that help concentrate the DSi intracellularly... 

Ion channel a specialized protein structure that spans biological membranes and, when open, permits the passage of specific ions. 

As individual G actin molecules are always oriented in the same direction relative to one another, F actin consequently has polarity, it has two different ends, at which polymerization takes place at different rates, if the ends are not stabilized by special proteins (as in muscle cells), then at a critical concentration of G actin the (+) end of F actin will constantly grow, while the (-) end simultaneously decays. These partial processes can be blocked by fungal toxins experimentally. Phalloidin, a toxin contained in the Amanita phalloides mushroom, inhibits decay by binding to the (-) end. By contrast, cytochalasins, mold toxins with cytostatic effects, block polymerization by binding to the (+) end. 

Modified amino acids, which occur in special proteins such as hydroxyproline in collagen and 3-methylhistidine in actin and myosin, can be used as indicators of the degradation of these proteins. 

Cobalamine can only be resorbed in the small intestine when the gastric mucosa secretes what is known as intrinsic factor—a glycoprotein that binds cobalamine (the extrinsic factor) and thereby protects it from degradation. In the blood, the vitamin is bound to a special protein known as trans-cobalamin. The liver is able to store vitamin Bi2 in amounts suf cient to last for several months. Vitamin B12 deficiency is usually due to an absence of intrinsic factor and the resulting resorption disturbance. This leads to a disturbance in blood formation known as pernicious anemia. 

Enzymes, specialized proteins, are used as designing tools for genetic engineering. One of these enzyme tools consists of restriction endonucleases that recognize a specific series of base pairs. They split the DNA at these specific points. This splitting is called lysing , which in reality is simply the hydrolysis of DNA units as shown in the following structure ... 

Another important defense tool of the immune system consists of specialized proteins called antibodies, or immunoglobulins, that are produced by lymphocytes and can recc nize and bind to proteins on the surfaces of microorganisms, resulting in their destruction and removal from the body. The disease-fighting lymphocytes that produce antibodies are able to remember previous exposure to a protein or other substance and respond quickly if it reappears in the body. Vaccination and other immunizations that prevent disease cause the immune system to develop the appropriate set of specific lymphocytes and antibodies that can quickly attack an infection. 

The green fluorescent protein is a specialized protein that has found many applications. Isolated from jellyfish, it has also been obtained by inserting the jellyfish gene in the genome of the tobacco plant (Boevink 1999). However, the process is still far from the efficiency needed by industry. 

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