Fibrous enzymic

Historically, dietary fiber referred to iasoluble plant cell wall material, primarily polysaccharides, not digested by the endogenous enzymes of the human digestive tract. This definition has been extended to iaclude other nondigestible polysaccharides, from plants and other sources, that are iacorporated iato processed foods. Cellulose [9004-34-6] (qv) is fibrous however, lignin [9005-53-2] (qv) and many other polysaccharides ia food do not have fiberlike stmctures (see also Carbohydrates). 

The natural polymers known as proteins make up about 15% by mass of our bodies. They serve many functions. Fibrous proteins are the main components of hair, muscle, and skin. Other proteins found in body fluids transport oxygen, fats, and other substances needed for metabolism. Still others, such as insulin and vasopressin, are hormones. Enzymes, which catalyze reactions in the body, are chiefly protein. 

Globular proteins are compact, are roughly spherical or ovoid in shape, and have axial ratios (the ratio of their shortest to longest dimensions) of not over 3. Most enzymes are globular proteins, whose large internal volume provides ample space in which to construct cavities of the specific shape, charge, and hy-drophobicity or hydrophilicity required to bind substrates and promote catalysis. By contrast, many structural proteins adopt highly extended conformations. These fibrous proteins possess axial ratios of 10 or more. 

The cytosol is the fluid compartment of the cell and contains the enzymes responsible for cellular metabolism together with free ribosomes concerned with local protein synthesis. In addition to these structures which are common to all cell types, the neuron also contains specific organelles which are unique to the nervous system. For example, the neuronal skeleton is responsible for monitoring the shape of the neuron. This is composed of several fibrous proteins that strengthen the axonal process and provide a structure for the location of specific membrane proteins. The axonal cytoskeleton has been divided into the internal cytoskeleton, which consists of microtubules linked to filaments along the length of the axon, which provides a track for the movement of vesicular material by fast axonal transport, and the cortical cytoskeleton. 

Fibroblasts have another and apparently contradictory capability—namely, the secretion of collagenase, the enzyme that initiates the dissolution of collagen. Mechanisms controlling the creation, extrusion, and deposition of fibrous extracellular components, and the synthesis of dissolution enzymes, are incompletely known. Each of these areas continues to be investigated (Furthmayr, 1982). 

For example, Escherichia coli have six PBP. PBP-la and -lb, which are transpepfidases, are involved in the synthesis of peptidoglycan. PBP-2 is necessary for supporting the rodshaped form of bacteria. Selective inhibition of this enzyme causes production of other non-rod-shaped forms of bacteria, which eventually undergo lysis. PBP-3 is necessary to form the partition during division. Selective inhibition of this enzyme leads to the formation of a fibrous form of bacteria containing many units of rod-shaped bacteria unable to separate one from another, which results in their death. Various beta-lactam antibiotics have a selective affinity to one or a few PBP. Inactivation of certain PBP (PBP-la, -lb, -2, or -3) causes cell death. Unlike these, inactivaition of low-molecular PBP (PBP-4, -5, and -6) is not lethal to bacteria. 

UNIT I Protein Structure and Function Chapter 1 Amino Acids 1 Chapter 2 Structure of Proteins 13 Chapter 3 Globular Proteins 25 Chapter 4 Fibrous Proteins 43 Chapter 5 Enzymes 53... 

The first protein structure to be learned was that of myoglobin, which was established by Kendrew et al. in I960.391-393 That of the enzyme lysozyme was deduced by Blake et al. in 1965.394 Since then, new structures have appeared at an accelerating rate so that today we know the detailed architecture of over 6000 different proteins395 with about 300 distinctly different folding patterns 396 New structures are being determined at the rate of about one per day. X-ray diffraction has also been very important to the study of naturally or artifically oriented fibrous proteins397 and provided the first experimental indications of the P structure of proteins. 

This experiment describes the preparation of a mitochondrial fraction from beef heart muscle. Heart muscle is an excellent choice of tissue because isolated mitochondria are stable and most enzyme activities remain high for a long period of time. Since heart muscle is more fibrous than other tissues, some problems are encountered in homogenizing the tissue. The preparation described here is suitable for the study of characteristic enzymatic activity, electron transport, and ADP phosphorylation. 

Protein research of this kind is important because all enzymes are proteins. They catalyze the speed of essential reactions in living systems, including the synthesis of protdns themselves. Knowledge of the dynamics of proteins will assist in better understanding those proteins that transport small molecules, electrons and energy to specific parts of an organism where they are needed. Those proteins of a structural nature, which make up fibrous tissue and muscle, also will be better understood. 

Most proteins may be divided into two groups fibrous and globular. Fibrous proteins usually serve structural roles. Globular proteins function as enzymes and in many other capacities. 

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