The Amino Acid Composition of Some

The Amino Acid Composition of Some Purified Proteins... 

Figure 9 shows the peptide maps and Table IV the amino acid compositions of some of the peptides. 

The amino acid composition of some )S-lg variants is shown in Table 4.4. It is rich in sulphur amino acids which give it a high biological value of 110. It contains 2 moles of cystine and 1 mole of cysteine per monomer of 18 kDa. The cysteine is especially important since it reacts, following heat denatura-tion, with the disulphide of K-casein and significantly affects rennet coagulation and the heat stability properties of milk it is also responsible for the cooked flavour of heated milk. Some /S-lgs, e.g. porcine, do not contain a free sulphydryl group. The isoionic point of bovine j3-lgs is c. pH 5.2. 

Thrombin has been purified by chromatographic techniques on IRC 50 columns. The amino acid composition of some thrombin preparations has been studied. Thrombin prepared from citrate-activated type I prothrombin lacks tryptophan and half cystine whereas thrombin prepared from extrinsic activation of type I prothrombin contains the 19 amino acids found in prothrombin. One molecule of thrombin contains one isoleucine N-terminal and one aspartic C-terminal [9]. 

G.R.Tristram and R.H. Smith, The Amino Acid Composition of Some Purified Proteins, Adv. Protein Chem. 18, 227-318 (1963). 

Muscle proteins in typical mammalian muscle tissue constitute around 20% of the muscle weight The major proportion of muscle is made up of muscle fibre proteins (elongated, threadlike cells) called myofibrillar proteins. Smaller amounts of soluble sarcoplasmatic proteins and insoluble structural proteins from connective tissue are also present (Table 2.16). Myofibrillar and sarcoplasmatic proteins are almost complete (whole) proteins, while the nutritional value of structural proteins is very low as they are almost indigestible. Table 2.17 gives the amino acid composition of some pure animal proteins Table 2.9 presents the amino acid compositions for the main types of meat proteins. 

Bolocera tuediae 283), and Pseudactinia varia 284). The amino acid composition of some of these toxins have been determined. 

In a review on membrane proteins, Guidotti (1972) has classified membranes into three types on the basis of their protein content. The first class is the simple, inert membrane represented by myelin. It consists primarily of lipid with little protein, acts as a permeability barrier and insulator, and has only three known enzymatic activities (Beck et al., 1968 Olafson et al., 1969 Kurihara and Tsukada, 1967 Gammer et al., 1976 Yandrasitz et al., 1976). The large second class of membranes which have a protein-to-lipid ratio of about 1 1 (w w) are typified by most mammalian plasma membranes. They have many enzymatic activities and sophisticated transport systems associated with them, in addition to the permeability factor. The third class of membranes has bacterial and inner mitochondrial membranes as its models. These membranes have proportionately larger amounts of protein than lipid and have added functions such as oxidative phosphorylation and nucleic acid synthesis. In general, the specialization and enzyme function of the membrane increases in proportion to its protein content. Table 4 gives the amino acid composition of some isolated membrane proteins. Total membrane protein (intrinsic + extrinsic) often has an amino acid composition which falls into the range of other nonmembrane, "soluble" proteins (Vanderkooi and Capaldi, 1972). 

To study the role of lysine residues in susceptibility to formalin fixation, the amino acid composition of immunoreactive peptides (to various monoclonal antibodies) was studied. Each peptide was evaluated to determine if immu-noreactivity was lost after formalin fixation. Formalin sensitivity was correlated with the peptides amino acid composition. The first step in the method is biopanning from a peptide combinatorial library with a monoclonal antibody. The peptides that bind to the antibody were tested for their sensitivity to formalin fixation. Some peptides remain immunoreactive whereas others do not. The peptides were then sequenced to look for differences between those that were sensitive to formaldehyde versus those that were not. The goal was to find whether there is a particular amino acid that is present in formalin-sensitive epitopes but absent in formalin-resistant epitopes, or vice versa. An advantage of this approach is that it is open-ended, without excluding any amino acids. 

Table 1.2 gives the average amino acid composition of some animal and vegetable proteins found in art and archaeology. 

The amino acid composition of milk lipid globule membranes, as determined by several groups, has been summarized elsewhere (Patton and Keenan 1975). Some differences are evident in the data from differ-... 

Hare, P. E. The amino acid composition of the organic matrix of some recent and fossil... 

FJ. Stevenson, Effect of some long-time rotations on the amino acid composition of the soil, Soil Sci. Soc. Am. Proc. 20 (1956) 204-208. 

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