Control amino acid composition

Formation of these drugs is under the direct control of a polypeptide adrenocorticotropic hormone (ACTH, corticotropin), which is processed by the anterior lobe of the hypophysis. Human ACTH consists of 39 amino acids and has a molecular weight of about 4500. It differs from animal ACTH in the amino acid compositions at positions 29-33. 

Figure 9.15. Overview of the production of Refludan (recombinant hirudin). The exact details of many steps remain confidential for obvious commercial reasons. A number of quality control checks are carried out on the final product to confirm the product s structure. These include amino acid composition, HPLC analysis and peptide mapping...

In the following I will present a model to tackle this question. We are at the level of speculations, but we will use some known facts. For example, let s start from the condensation of NCA-anhydrides, a reaction which, as we have seen in the previous chapter, is considered prebiotic. In this way, oligopeptides up to (say) a length of ten can be built, possibly under thermodynamic control, but starting from a definite set of conditions (amino-acid composition in the starting mixture, pH, salinity, etc.). We can assume, and this is actually quite reasonable, that in this way copious libraries of different decapeptides have been formed, each in a significant concentration. 

The heterostranded coiled coil shown in Figure 4 and similar molecules were designed to examine the role of interchain hydrophobic interactions in controlling the formation and stabilization of coiled coils. The question addressed was whether two Leu-Ala interactions provided more stability to the coiled coil as a heterostranded molecule than the two homostranded coiled coils which differ by having a Leu-Leu and Ala-Ala interaction. These homo- and heterostranded coiled coils have the identical amino acid composition overall and in the hydrophobic core that stabilizes the coiled-coil structure. The only difference is in the sequence of the core residues. 

The final product is controlled by electrospray ionization mass spectroscopy. If the mass obtained does not correspond to that predicted for the chemokine with the formation of two disulfide bonds, amino terminal sequencing and amino acid composition analysis is used to identify possible mutations. 

By contrast, the amino acid compositions of the two forms of inver-tase (internal and external) differ significantly in the number of residues of certain amino acids. These differences occur notably in the content of serine, alanine, cystine, methionine, tyrosine, lysine, and histidine. The significance of these differences is not yet apparent, but these two invertases are obviously not isoglycoenzymes. The synthesis of proteins having such diverse amino acid compositions as have the two invertases would probably necessitate two separate genetic-control mechanisms. 

NH2-temiinus resulting in a mass of about 30 IdD and 3) an external peptide standard (450 pmol) that was provided dry in an eppendoiftube and that had the same amino acid composition as the unique tryptic peptide insert but whose sequence was randomized. In the case of the two protein samples, 70 pmol of each had been subjected to SDS PAGE and were supplied either as Coomassie Blue stained gel slices or as a section of amido black stained PVDF membrane. In the case of the PVDF samples, an oversize piece of PVDF was included so that a section could be used as a digest control, and in the case of the gel samples, a blank section of gel was included for the same purpose in a separate eppendorf tube. 

Several examples have shown that the degree of activity resulting from synthesis is reproducible, as is the amino acid composition. In other cases, e.g., with p-nitrophenyl acetate, activity was quite variable. Nearly total inactivation by heat in aqueous solution has been demonstrated for some pyropolyamino acids other such systems are heat-stable in aqueous solution. In the p-nitrophenyl acetate system, the nature of the heat inactivation, if not the mechanistic reason for enhanced activity, is understood to involve both imide and imidazole residues. Differing interactions of these residues to produce loci of varying degrees of efficiency could help to explain the quantitative nonreproducibility of activity in separate syntheses. With OAA, selectivity of action was strict, in that several a-keto acids were not measurably acted upon under controlled conditions. The identification of the active locus for hydrolysis of the substrate p-nitrophenyl acetate supports the general inference of specificities, inasmuch as similarly prepared polymers have been shown not to be operative for other reactions, e.g., decarboxylation of OAA (17). 

Hyllner, S.J., H.F.-P. Barber, D.G.J. Larsson and C. Haux. Amino acid composition and endocrine control of vitelline envelope proteins in European sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata). Mol. Reprod. Dev. 41 339-347, 1995. 

The role of proteins as enzymes in controlling a cellular activity was known much before its structure was elucidated. The conceptual breakthrough in deciphering the structure of a protein as a linear array of amino acids came from the enunciation of the one-gene enzyme concept. This conceptual breakthrough was materialized by certain technical advances. The technical advances included the development of machines for the analysis of the amino acid composition and for the determination of the sequence of the amino acids in a protein. With the help of these machines, the structure of proteins was elucidated one protein at a time for several years. Later,... 

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