Silk fibroin acids

The percentages of amino acids in silk fibroin which Poison et al. (224) found by direct visual and indirect photometric analysis of ninhydrin paper-partition chromatograms are shown in Table VII. The percentages obtained for alanine, glycine, and serine appear to be reasonably accurate, inasmuch as they agree closely with those found by other methods. It would be of interest to determine alanine by the microbiological method reported recently by Sauberlich and Baumann (238), in view of the widely different values found for this amino acid by the described ninhydrin-chromatographic procedure and the selec-... 

Table VII. Percentages of Amino Acids in TnSIrMtRnlnr Direct Color Analysis Silk Fibroin literature ...

Resilin has a greater percentage of acidic residues than collagen, elastin, and silk fibroin and contains fewer non-polar residues (i.e., Gly, Ala, Val, He, Leu, Pro, Met, and Phe) than silk fibroin and elastin. The significant content of acidic residues might account for resilin s hydrophilicity as well as its low isoelectric point, as indicated through swelling experiments [141, 145]. Resilin contains little to no... 

Results of amino acid analysis performed on resilin from the locust Schistorcerca gregaria, compared with values for collagen, elastin, and silk fibroin. Reproduced from [145] with permission from Elsevier, copyright Elsevier 1961 Includes 106 hydroxyproline and 7 hydroxylysine... 

The bacterial resistance of silk fibroin can be improved by treatment at low pH values in aqueous solutions of metal ions and at high pH values in solutions of metal-amine complexes, using untreated silk or silk pretreated with an aqueous solution of tannic acid (10.183). Suitable metals include Cu, Zn, Ni, Fe and Ag [533]. It is to be expected that treatment with such metal compounds will be subject to restrictions in environmentally sensitive areas. 

Besides the previously mentioned collagen, a wide variety of natural polymers have been involved in the synthesis of bio-nanohybrid materials with potential application in bone repair and dental prostheses. For instance, some recent examples refer to bionanocomposites based on the combination of HAP with alginate [96,97], chitosan [98,99], bovine serum albumin (BSA) [100], sodium caseinate [101], hyaluronic acid [102], silk fibroin [103,104], silk sericin [105], or polylactic add (PLA) [106,107]. These examples illustrate the increasing interest in the subject of HAP-based biohybrid materials, which has led to almost 400 articles appeared in scientific journals in 2006 alone. 

Amino acid Egg white Egg yolk Casein Animal glue (collagen) Wool (keratin) Silk (fibroin) Garlic... 

An amperometric urate sensor based on uricase-immobilized silk fibroin membrane was developed by Zhang [256], The biosensor can be used to measure the urate level in human serum or urine and standard additions of uric acid. F or this biosensor, the recoveries of uric acid in human serum and urine are in the range of 94.2 102.6% to 92.5 97.9%, respectively. The relative standard deviations for repeatedly monitoring standard urate solution, human serum, and urine are 2.37, 3.72, and 2.95%, respectively, based on 100 measurements. 

Y.Q. Zhang, W.D. Shen, R.A. Gu, J. Zhu, and R.Y. Xue, Amperometric biosensor for uric acid based on uricase-immobilized silk fibroin membrane. Anal. Chim. Acta 369, 123-128 (1998). 

Ha, S. W., Gracz, H. S., Tonelli, A. E., and Hudson, S. M. (2005). Structural study of irregular amino acid sequences in the heavy chain of Bombyx mori silk fibroin. Biomacromolecules 6, 2563-2569. 

Silk fibroin contains no cystine and the content of lysine and histidine is also low (about 1% in total), but it does contain tyrosine phenolic (13%) and serine alcoholic (16%) sidechains. Since glycine accounts for 44% of the total aminoacid content, an N-terminal glycine residue is reasonably representative of most of the primary amino dyeing sites in silk fibres. Amino acid analysis of hydrolysed reactive-dyed silk indicates that the reaction between fibroin and reactive dyes takes place mainly at the e-amino group of lysine, the imino group of histidine and the N-terminal amino group of the peptide chain. In an alkaline medium, the hydroxy groups of tyrosine and serine also react [114]. 

In 1923, Brill obtained some excellent diffraction patterns on silk fibroin and concluded that there were eight amino acid residues in its unit cell (51). Further challenging Herzog, Weissenberg discussed the possibility of long chains in 1925 (52). While at the same time J. R. Katz discovered that the diffraction pattern of stretched rubber indicated that partial... 

Silk is produced from the spun threads from silkworms (the larvae of the moth Bombyx mori and related species). The main protein in silk, fibroin, consists of antiparallel pleated sheet structures arranged one on top of the other in numerous layers (1). Since the amino acid side chains in pleated sheets point either straight up or straight down (see p. 68), only compact side chains fit between the layers. In fact, more than 80% of fibroin consists of glycine, alanine, and serine, the three amino acids with the shortest side chains. A typical repetitive amino acid sequence is (Gly-Ala-Gly-Ala-Gly-Ser). The individual pleated sheet layers in fibroin are found to lie alternately 0.35 nm and 0.57 nm apart. In the first case, only glycine residues (R = H) are opposed to one another. The slightly greater distance of 0.57 nm results from repulsion forces between the side chains of alanine and serine residues (2). 

Silk-fibroin is composed of practically only three amino acids, glycine, alanine and tyrosine, and is probably the simplest protein known. It resembles the fibroin of spider s silk very closely, but here the presence of so much glutamic acid is one of the characteristics. 

The results of numerous investigations were published in i860 by Stadeler, who found tyrosine in silk-fibroin, mucin and various other proteins, and who also noted its occurrence in the free state in various organs, generally in conjunction with leucine. Since then, tyrosine has been constantly obtained from proteins by hydrolysis with acids and by the action of trypsin, and has long been regarded as a constituent of the protein molecule. 

Glycine A non-essential amino acid. It is found primarily in gelatin and silk fibroin and used therapeutically as a nutrient. It is also a fast inhibitory neurotransmitter. [NIH]... 

Some protein structures limit the kinds of amino acids that can occur in the J3 sheet. When two or more /3 sheets are layered close together within a protein, the R groups of the amino acid residues on the touching surfaces must be relatively small. J3-Keratins such as silk fibroin and the fibroin of spider webs have a very high content of Gly and Ala residues, the two amino acids with the smallest R groups. Indeed, in silk fibroin Gly and Ala alternate over large parts of the sequence. 

Ala Alanine Clfe—CII—COOII NEUTRAL AMINO ACIDS ALIPHATIC TYPE 1879 by Schutzenberger 1888 by Weyl (silk fibroin) 6.0... 

It is well known that well-ordered (3-chitin (a polysaccharide) associated with a less ordered protein in the (3-sheet conformation is the main component of nacreous organic matrix in shell. The amino acid sequence of such proteins is very similar to those of silk fibroins. Indeed, the amino acid sequence of a major protein from the nacreous shell layer of the pearl oyster resembles that of spidroin (Sudo et al., 1997 Weiner and Traub, 1980). The question of whether silk-like proteins play an important role in shell formation is raised. When Falini et al. (1996) did the experiment with the proteins from the shell, they assembled a substrate in vitro that contained (3-chitin and natural silk fibroin and concluded that the silk fibroin may influence ion diffusion or the accessibility to the chi tin surface or both. Furthermore, cryo-TEM study of the structure of the Atrina shell nacreous organic matrix without dehydration... 

Zhou, C.Z., Confalonieri, F., Jacquet, M., Perasso, R., Li, Z.G., and Janin, J. "Silk fibroin Structural implications of a remarkable amino acid sequence". Proteins Struc Fund. Genet. 44(2), 119-122 (2001). 

Raney nickel has been modified with amino acids and other chiral reagents to give catalysts that have been used to effect asymmetric reductions (7). However, these catalysts suffer from some of the same kinds of vagaries that have been observed for the palladium on silk fibroin catalysts. For example, the optical purities of the products were found to be very dependent on pH and the method of catalyst preparation. 

The basic amino acids of silk fibroin. Determination of the basic amino acids yielded by proteins. Ibid., 93, 105 (1931). With H. B. Vickery. 

The (3-strand sequences are stretched out conformations of these polypeptide sections and are typically stabilized by inter-strand hydrogen bonds between keto (C = 0) oxygens and peptide bond NHs, the strands being arrayed in an antiparallel fashion. This type of secondary structure is favoured by amino acid residues with small R groups (such as Gly, Ala and Ser) that minimize steric overlap between chains. Thus a well-known protein having this type of secondary structure is silk fibroin that has a high proportion of repeated sequences involving Gly, Ala and Ser and an extensive antiparallel (3-pleated sheet structure. The macroscopic properties of silk fibroin (flexibility but lack of stretchability) reflect this type of secondary structure at the molecular level. 

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