Proteins basic properties

The fundamental role of blood in the maintenance of homeostasis and the ease with which blood can be obtained have meant that the study of its constituents has been of central importance in the development of biochemistry and clinical biochemistry. The basic properties of a number of plasma proteins, including the immunoglobulins (antibodies), are described in this chapter. Changes in the amounts of various plasma proteins and immunoglobulins occur in many diseases and can be monitored by electrophoresis or other suitable procedures. As indicated in an earlier chapter, alterations of the activities of certain enzymes found in plasma are of diagnostic use in a number of pathologic conditions. 

Another basic property of solenoids is their twist. This parameter reflects the fact that successive coils are not stacked exactly above one another but with a small angular offset. Twist may be defined in relation to reference points at corresponding positions in consecutive coils (Fig. 1A). When connected, these points form a helix. The sense of the twist is given by the hand of this helix as it winds around the solenoid axis. Note that the definition of protein solenoid twist (Kobe and Kajava, 2000) differs from the usual definition of the twist in /1-sheets which is defined by the twist of /(-strands... 

The ion formation may occur in the bulk solution before the electrospray process takes place or in the gas phase by protonation or salt adduct formation, or by an electrochemical redox reaction. Polar compounds already exist in solution as ions therefore, the task of the electrospray is to separate them from their counterions. This is the case of many inorganic and organic species and all those compounds that show acidic or basic properties. Proteins, peptides, nucleotides, and many other bio- and pharmaceutical analytes are typical examples of substances that can be detected as proto-nated or deprotonated species. 

For application of a biocatalyst we must know its basic properties, the substrate specificity and the kinetic characteristics. The substrate specificity is a relatively uncomplicated topic, it can be determined with simple experiments, and for the most important enzymes many data are available. Determination of the kinetic properties of an enzyme is a more complex problem. A detailed description of an enzymic catalysis requires extensive data about the stracture of the whole protein molecule, the stracture of... 

Most of the basic properties of RNase XL are summarized in Tables II and IV. It is an acidic protein, most active at pH 4.5 for RNA digestion (7). It has far less hydrolase activity than phosphotransferase activity (SO). The enzyme preparation obtained possesses a specific activity of about 1.4 X 103 units per OD280 unit, corresponding to about one-fifth that of RNase Tj and twice of that of RNase T2. 

Milk proteins are subdivided into random coiled caseins, which can be precipitated by acidification of raw skim milk to pH 4.6 at 20°C, and into more globular whey proteins, which remain in the serum after precipitation of the caseins (42). In Table 8, an overview is given of the molecular structure and basic properties of the major protein fractions present in milk. Some specific properties that might be of importance for their determination in foods and food products are also listed. For the young of mammals, including humans, milk is the first and, for most, the only food ingested for a considerable period of time. With the domestication of animals, it became possible to include milk in the diet of adult humans as well. For much of the world, particularly in the West, milk from cattle (Bos taurus) accounts for nearly all the milk processed for human consumption (43). 

Certain acidic and basic properties are common to all amino acids found in proteins except for the amino acid proline. 

Table 1. Basic properties of radioactive labels of proteins...

Other parts of the protein molecule, such as the peptide group, also possess acidic or basic properties, but they are not titrated within the range of pH 1.5 to 12, within which titration studies are usually confined. Protein molecules tend to become degraded outside this range of pH.)... 

Wool and silk. Wool is animal hair from the body of sheep. Silk is a lustrous, tough elastic fiber produced by silkworms. Both wool and silk fibers are protein substances with both acidic and basic properties. The building blocks for these fibers are amino acids. The a amino acids... 

The DNA in eukaryotic chromosomes is not bare. Rather eukaryotic DNA is tightly bound to a group of small basic proteins called histones. In fact, histones constitute half the mass of a eukaryotic chromosome. The entire complex of a cell s DNA and associated protein is called chromatin. Five major histones are present in chromatin four histones, called H2A, H2B, H3, and H4, associate with one another the other histone is called HI. Histones have strikingly basic properties because a quarter of the residues in each histone is either arginine or lysine. 

Proteins have both acidic and basic properties because of their amino (basic) and carboxyl (acidic) groups at the ends of the peptide chain. It is therefore possible for proteins to combine with both acids and bases, enabling them to function as buffers. 

Synthetic iron-sulfur clusters have weakly basic properties and accept protons with a pX of from 3.9 to 7.4. Similarly, one clostridial ferredoxin, in the oxidized form, has a pX of 7.4 it is shifted to 8.9 in the reduced form. If we designate the low-pH oxidized form of such a protein as HOx and the reduced form as HRed, we can depict the reduction of each Fe4S4 cluster as follows. 

This chapter reviews several techniques which combine the use of laser microbeams with antibodies to study molecular and cellular biology. An overview of the basic properties of lasers and their integration with microscopes and computers is provided. Biophysical applications, such as fluorescence recovery after photobleaching to measure molecular mobility and fluorescence resonance energy transfer to measure molecular distances, as well as ablative applications for the selective inactivation of proteins or the selective killing of cells are described. Other techniques, such as optical trapping, that do not rely on the interaction of the laser with the targeting antibody, are also discussed. 

All these activities appear to be driven by the basic property of Hsp70s to interact with short hydrophobic peptide segments of protein substrates in an ATP-dependent fashion. The broad spectrum of cellular functions of Hsp70 proteins is achieved through three strategies. First, the amplification and diversification of hspK) genes in evolution... 

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