Amino Acid Composition, Subunits

As an alternative to these established methods, the derivatization of amino acids with the subsequent separation and detection of derivatives is possible (pre-column derivatization). Various derivatization reagents can be selected, such as  

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Robin, Y. Guillou, A. Thoai, N.V. Unspecific arginine kinase of molecular weight 150 000. Amino acid composition, subunit structure and number of substrate binding sites. Eur. J. Biochem., 52, 531-537 (1975)... 

Most enzymes consist of several identical or different subunits. It is known that subunits of similar activity but different origin, which therefore differ in size and amino acid composition and sequence, replace each other in oligomeric enzymes, leading to the formation of enzyme chimeras of catalytic activity 47). The feasibility... 

Related behaviour to that just described occurs in haemoglobin, although the latter is a tetramer consisting of four subunits each containing an iron porphyrin. The latter are located within hydrophobic pockets in the globin portion of the molecule (which, in this case, is composed of four linked chains - consisting of two a and two / chains, which differ in their respective amino acid compositions). 

Milk XO has a molecular weight of c. 300 kDa and consists of two subunits. The pH optimum is about 8.5 and the enzyme requires flavin adenine dinucleotide (FAD), Fe, Mo and an acid-labile compound as co-factors cows deficient in Mo have low XO activity. The amino acid composition of XO has been determined by a number of workers at least five genetic polymorphic forms have been reported. 

Starnes, W.L. Munk, P. Maul, S.B. Cunningham, G.N. Cox, D.J. Shive, W. Threonine-sensitive aspartokinase-homoserine dehydrogenase complex, amino acid composition, molecular weight, and subunit composition of the complex. Biochemistry, 11, 677-687 (1972)... 

Piez, K. A., Eigner, E. A., Lewis, M. S. The chromatographic separation and amino acid composition of the subunits of several collagens. Biochemistry 2, 58 (1963)... 

The amino acid compositions of each subunit and the native enzyme are shown in Table 5. There are distinct differences between the two subunits. As would be expected from the isoelectric points, the a subunit contains more acidic amino acids than the /3 subunit does, and the /3 subunit contains more basic amino acids than the a subunit does. The amino acid composition of the native enzyme obtained by actual analyses agrees quite well with that calculated from the compositions of the a and /3 subunits, based on the assumed subunit structure of (a ls- These results confirms the assumption that the native enzyme consists of 8 protomers, each of which is composed of a pair of two non-identical subunits (a2fi2)97 I0S. ... 

The enzyme, which has been isolated from many species, is a tetramer of Mr 140 000. The two forms of the enzyme, the H4, predominating in heart muscle, and the M4, predominating in skeletal muscle, give rise to a family of isozymes.46,47 The amino acid composition of the polypeptide chain that constitutes the M4 form is significantly different from that of the H4 form, and the two have different kinetic properties. Despite this, the sites for the association of the subunits had to... 

Analysis in two different laboratories of the amino acid composition of the enzyme crystallized from ethanol gave similar results with the exception of the values for cysteine. Hausmann (11) found only a trace, but Eifler et al. (12) reported 3 cysteine residues per mole of 60,000 molecular weight. The latter investigators found that three different sulfhydryl reagents reacted with the enzyme in amounts approaching one mole per mole of enzyme. A total of three -SH per mole were found after reduction with sodium borohydride. The investigators suggested that the molecule contains one -S-S- and one -SH, which, if true, forbids identity of subunits. 

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... 

Amino acid analysis of peanut proteins revealed that the principal amino acids were glutamic acid, 22-27% arginine, 11-13% and aspartic acid, 8-13% (Oslova et al., 1973). Cation-exchange HPLC and amino acid analyzer results showed differences in the content of phenylalanine and tyrosine, which were lower when analyzed by cation-exchange HPLC (Eukin and Griffith, 1983). The amino acid composition of six subunits of arachin was reported by Yamada et al. (1979). Bhushan and co-workers... 

The review describes amino acid composition, molecular weights of subunits, fluorescence emission and UV spectra, a 201-amino acid residue sequence of one of the subunits, titration curve and polarograms showing effects of zinc and copper concentrations on diffusion current depression with respect to arachin. In all, there are 108 references in the bibliography. 

The first evidences for a stimulatory role of GTP in regulation of adenylyl cyclase systems were published in 1971 [1,2]. By 1980 a separate component, responsible for mediation of hormonal stimulation of adenylyl cyclases, had been purified [3]. This component, initially referred to as G/F and Ns, is now called Gs. It is a het-erotrimeric complex composed of a subunits that migrate on SDS-PAGE at 42 and 52 kDa [3], (3 subunits of ca. 35 kDa [3], and y subunits of 6-10 kDa [4] (For reviews see Refs. 5 and 6). Its a subunits are ADP-ribosylated by CTX [7], dissociate from the holocomplex after activation [8,9] and hydrolyze GTP [10]. The a subunits have been cloned in several laboratories [11-17] and their amino acid composition has been deduced from the cDNA nucleotide sequence. The amino acid sequence of one of two types of /3 subunits, called /336 [18], has also been deduced from its cDNA [19-21]. The amino acid sequence of the y subunit is not yet known. 

As pointed out earlier in this article, T differs from other G proteins in that it is a peripheral membrane protein. After activation by Rho it seems to undergo subunit dissociation in which both its a subunit and its /3y complex dissociate from the Rho-containing membranes. Purification of brain G-proteins has shown that free a subunits of G0 and Gj are also water soluble, remaining in solution in the absence of detergents [74], The hydrophobicity of the whole ajSy G and Gj complexes was shown to be due to their j8y complexes 189]. Indeed, purified a subunits associate with phospholipid vesicles only if j8y complexes have been incorporated during vesicle formation [189]. Since the amino acid composition of T-/3 is equal to that of other G-j8s, but their ys differ, it follows that the principal role of y subunits should be to anchor non-T G proteins to the plasma membranes. This conclusion assumed, of course, that j8 subunits are not post-translationally modified in a tissue specific manner such that that they become water soluble in retinal photoreceptor cells and... 

Creatine kinase functions as a dimer. The dimer can consist of combinations of two different subunits, M and B. Different cell types produce or express the MM, MB, or BB forms of CK. Although the amino acid composition of the M and B subunit differ, all three dimeric forms can catalyze the reaction described above. Different forms of an enzyme that catalyze the same reaction (such as the MM, MB, and BB forms of CK) are referred to as isoenzymes. 

Myosin. Rabbit muscle myosin is a long, thin molecule (VI400 X 20-50 A) with a molecular weight of 5 X 10. It is composed of two heavy chains and four light chains as demonstrated by SDS-polyacrylamide disc gel electrophoresis. On tryptic digestion, myosin is split into the subunits, H-meromyosin (HMM) and L-mero-myosin (LMM). HMM is further split into S-l and S-2 subunits. While LMM is a rod of V)0% a-helical content, the a-helical content for HMM, S-l and S-2 fragments is 46%, 33% and 87%, respectively. The ATPase activity is localized in the S-l subunit (33,34). Although fish myosins appear to have the same structural profile (10,22,35-40) and similar amino acid composition as rabbit myosin (39,41,42), fish myosin is different from rabbit myosin in physicochemical properties such as solubility, viscosity and stability (10,22,35-40). 

In 1983, Kono and Fridovich reported the isolation of a pseudocatalase from L. plantarum which contained manganese (159). The enzyme was 172 kDa the original report gave a subunit of 28.3 kDa and 1.12 0.37 atoms of manganese per subunit. The visible spectrum of the enzyme displayed an absorption maximum at 470 nm (e = 1.35 x 103 M l cm-1) with shoulders at 398 and 500 nm. This spectrum is extremely similar to those of Mn superoxide dismutases (Section II,A) and, thus, indicative of the presence of Mn(III). Comparison of the amino acid compositions of the two enzymes suggested that they are not closely related. The pseudocatalase possessed no superoxide dismutase activity but had a turnover number of 3.9 x 10s mol of peroxide per mole of enzyme per second. 

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