Molecular weights storage proteins

The measurements of the labeled metabolites may be performed with GC- or LC-MS, or by NMR. Because it is the most commonly used method, we will only consider GC-MS based approaches here. Obviously and unfortunately, it is not possible to directly measure the isotopomer enrichments by GC-MS, because the apparatus only yields total masses of molecules or fractions thereof, but not directly the position of a label. Each MS peak is produced by all isotopomers with the same molecular weight that is, the same number of labeled carbon positions. Sometimes this concept is also called mass isotopomers [264]. In a so-called retrobiosynthetic approach, it has been shown that the labeling state of many intracellular pools can be determined indirectly by measuring the labels in macromolecular biomass components at steady state for example, the labeling state of alanine from hydrolyzed protein reflects the label of pyruvate [265]. Using this approach, it is possible to quantify fluxes into storage components. 

Macromolecules are very much like the crystalline powder just described. A few polymers, usually biologically-active natural products like enzymes or proteins, have very specific structure, mass, repeat-unit sequence, and conformational architecture. These biopolymers are the exceptions in polymer chemistry, however. Most synthetic polymers or storage biopolymers are collections of molecules with different numbers of repeat units in the molecule. The individual molecules of a polymer sample thus differ in chain length, mass, and size. The molecular weight of a polymer sample is thus a distributed quantity. This variation in molecular weight amongst molecules in a sample has important implications, since, just as in the crystal dimension example, physical and chemical properties of the polymer sample depend on different measures of the molecular weight distribution. 

A typical molecular analysis of various micro-organisms is shown in Table 5.9U ) Most of the elemental composition of cells is found in three basic types of materials—proteins, nucleic acids and lipids. In Table 5.10, the molecular composi-tion of a bacterium is shown in more detail. Water is the major component of the cell and accounts for 80-90 per cent of the total weight, whilst proteins form the next most abundant group of materials and these have both structural and functional properties. Most of the protein present will be in the form of enzymes. Nucleic acids are found in various forms—ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Their primary function is the storage, transmission and... 

Protein is formed mainly of polymerised amino-acids. The primary structure, unlike that of synthetic polymers, is non-repetitive and, for its production, requires a chemical template stored in the structure of the DNA molecule. The sizes of proteins vary considerably (in a range of molecular weights from 6000 to 1,000,000). Proteins fulfill many roles within the cell, the most important of which is that of catalysis. Proteins which have catalytic activity are called enzymes whilst other proteins have important roles in storage, transport, protection (antibodies), as chemical messengers (hormones) and in structure 17,, 8). 

Calsequestrin is a calcium-storage protein found in the sacroplasmic reticulum, which binds about 50 calcium ions per monomer (molecular weight 40 000) with binding constants in the range 103-105 dm3 mol. Release and uptake of Ca2+ during muscle contradion and relaxation involve this store. Calsequestrin from rabbit skeletal muscle has a random coil conformation in the absence of calcium. Binding of Ca2+ is associated with a change to a more compact structure.267... 

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