Differences in Amino Acid Composition

The proteins of different cereal flours vary in their amino acid composition (Table 15.10). Lysine content is low in all cereals. Methionine is also low, particularly in wheat, rye, barley, oats and corn. Both amino acids are significantly lower in flour than in muscle, egg or milk proteins. By breeding, attempts are being made to improve the content of all essential amino acids. This approach has been successful in the case of high-lysine barley and several corn cultivars. 

Cereal variety Husk Bran Germ Endosperm 

In 1907 Osborne separated wheat proteins, on the basis of their solubility, into four fractions. Sequential extraction of a flour sample 

Further separation of the Osborne fractions and subfractions into the components is possible analytically with electrophoretic methods (cf. Fig. 15.3, 15.4) and analytically andpreparatively with RP-HPLC (cf Figs. 15.5-15.8). 

Fraction Minerals Thiamine Riboflavin Niacin Pyridoxal phosphate Pantothenic acid 

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The hide proteins differ in amino acid composition and physical stmcture. The principal amino acids (qv) of the hide proteins are hsted in Table 1. Of particular importance is the difference in the water solubiUty of the proteins. AH of the proteins are soluble in water when heated, and upon the addition of either strong acids or bases. Proteins (qv) are amphoteric, possessing both acid and base binding capacity. 

The fifteen samples analyzed for amino acid composition were compared to a human type 1 collagen standard. There are no significant differences in amino acid composition among these samples, which range in age from stillbirth to adult. Analytical error is 10%. All samples show the typical composition of type 1 collagen (Table 1.1). Based on these results there is no reason to suspect differential preservation of specific amino acids in the small bones of infants in comparison to bones of adults and older children. 

D. Isozymes are protein-based enzymes that catalyze the same reaction but differ in amino acid composition. 

Mattil (36) emphasized the difference in amino acid composition within the two classifications for commercial products. He pointed out that some of the differences are deliberate a high solubility isolate could well have a different amino acid composition than an isolate with low solubility. Mattil evaluated isolate PER s, which ranged from... 

Differences in protein function result from differences in amino acid composition and sequence. Some variations in sequence are possible for a particular protein, with little or no effect on function. 

At least two distinct FDPases are found in animal tissues, one in liver and kidney, and the other in white muscle. The liver and kidney enzymes show minor differences in amino acid composition and in their response to agents, such as pyridoxal phosphate (4%), but these differences may be the result of modification during isolation (see above). On the other hand, the muscle enzyme is distinctly different in immunological properties as well as in amino acid composition (63, 74). All of the mammalian FDPases are similar in having a molecular weight of approximately 135,000, and all are composed of four subunits the... 

Singh and Preiss265 concluded that, although some homology exists between the three starch-branching enzymes, there are major differences in the structure of BEI when compared to BEIIa and BEIIb, as shown by its different reactivity with some monoclonal antibodies and differences in amino acid composition and proteolytic digest maps. 

The disparity in these conclusions may reside in differences between bovine Gj and porcine Gs not detectable by simple SDS-PAGE migration. Indeed, a cDNA encoding bovine brain aj [86] and a cDNA encoding porcine brain a [87] show significant differences in amino acid composition in spite of large stretches of identity (see below). 

The modern ion-exchange methods for amino acid analysis are po ibly more accurate, and certainly more reliable than microbiological procedures with careful use the experimental variations are small and the methods are sufficiently reliable to show up small differences in amino acid composition where comparative surveys are carried out in the same laboratory under identical conditions. Gk)tte et al. (1961) used the method of Moore and Stein... 

The proteins about to be discussed exhibit, as a common feature of their rotatory dispersions, a departure from the covariance of the rotatory parameters characteristic for a simple mixture of helical and disordered regions. Because of differences in amino acid composition and the sensitivity of the denatured form to solvent conditions, some lack of correspondence between the optical rotation at a single wavelength, [m ]x, and its change on denaturation, with the other dispersive parameters, c, 5o,... 

Keratinized tissues contain several types of cells and these cells in turn contain many protein constituents. It is possible therefore for keratins to differ in amino acid composition either because the constituent proteins differ or because of differences in the relative amounts of identical proteins. It is rarely possible therefore to relate differences in over-all amino acid composition to differences in character or content of a particular protein constituent. 

It is probable that Bailey s first interest in the muscle field, in which lies his greatest contribution, was aroused by the work of Astbury and Dickinson who showed that fibers of denatured myosin behaved in ways similar to keratin so far as their elastic properties were concerned and their structures were revealed by X-ray analysis. At this time the Chibnall group was much interested in the amino acid composition of proteins. The obvious similarities in fibrous behavior between keratin and myosin despite their differences in amino acid composition, particularly in cystine content, stimulated Bailey to make a comparative study of the composition of some of the then recognized muscle proteins. This was Bailey s first paper on muscle and extension of the... 

Enzymes which exist in multiple forms within a single species of organism or even in a single cell are called isoenzymes or isozymes. Such multiple forms can be detected and separated by gel electrophoresis of cell extracts. Since they are coded by different genes, they differ in amino acid composition and thus in their isoelectric pH values. Lactate dehydrogenase is an example for the isoenzymes which occur as five different forms in the tissues of the human and other vertebrates. All the five isozymes catalyze the same reaction. 

The amino acid composition of connectin is listed in Table IV. It is an acidic protein rather similar to actin. There are hardly any recognizable differences in amino acid composition between j8-connectin and a-con-nectin-rich samples. It is of some interest to note that C protein (MW 135 kDa) located on myosin filaments has an amino acid composition similar to connectin (Offer et al., 1973). Immunological tests showed that the two proteins are distinguishable. 

On electrophoresis at pH 5.4, the albumin of the domestic fowl separates into three components — fast, slow, and mixed types (M5). It is not known whether these are true isoalbumins with slight differences in amino acid composition or artificially induced forms with realigned intramolecular hydrogen bonding. Some electrophoretic separation of fowl albumins is... 

A rapid FTIR method for the direct determination of the casein/whey ratio in milk has also been developed [26]. This method is unique because it does not require any physical separation of the casein and whey fractions, but rather makes use of the information contained in the whole spectrum to differentiate between these proteins. Proteins exhibit three characteristic absorption bands in the mid-infrared spectrum, designated as the amide I (1695-1600 cm-i), amide II (1560-1520 cm-i) and amide III (1300-1230 cm >) bands, and the positions of these bands are sensitive to protein secondary structure. From a structural viewpoint, caseins and whey proteins differ substantially, as the whey proteins are globular proteins whereas the caseins have little secondary structure. These structural differences make it possible to differentiate these proteins by FTIR spectroscopy. In addition to their different conformations, other differences between caseins and whey proteins, such as their differences in amino acid compositions and the presence of phosphate ester linkages in caseins but not whey proteins, are also reflected in their FTIR spectra. These spectroscopic differences are illustrated in Figure 15, which shows the so-called fingerprint region in the FTIR spectra of sodium caseinate and whey protein concentrate. Thus, FTIR spectroscopy can provide a means for quantitative determination of casein and whey proteins in the presence of each other. 

Detailed chemical investigation of the parvalbumins began with the demonstration that the low molecular weight myogens of carp white muscle were composed of three components, designated as 2, 3 and 5, which could be separated electrophoresis (102). These proteins were not present in red muscle of cod (102), demonstrating a protein difference between the two types of muscle. The three cod parvalbumins have been crystallized (103) and their amino acid composition has been determined. The three proteins have only small differences in amino acid composition, molecular weight and other physical properties. 

Cytochrome P-450 LM4 I and cytochrome P-450 LM4 II showed the same apparent molecular weight and spectral properties as the original cytochrome P-450 LM4 fraction. However, the two subfractions differed in amino acid composition. 

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