Amino acids base hydrolysis

Figure 25.1. Salvage and de Novo Pathways. In a salvage pathway, a base is reattached to a ribose, activated in the form of 5-phosphoribosyl-1-pyrophosphate (PRPP). In de novo synthesis, the base itself is synthesized from simpler starting materials, including amino acids. ATP hydrolysis is required for de novo synthesis.

Amino acid analysis, determination of amino acid composition of a peptide by complete hydrolysis followed by the quantitative analysis of the liberated amino acids. For hydrolysis, numerous chemical and enzymatic protocols are known. Based on the pioneering studies of Stein and Moore, amino acid analysis has been automated. Nowadays, instmments are in use for quantitative amino acid analysis which are based on partition chromatography, such as HPLC and gas-liquid chromatography [S. Blackburn, Amino Add Determination, M. Dekker, New York, 1978 ... 

New Procedure for Isolation of Amino Acids Based on Selective Hydrolysis of Trimethylsilyl Derivatives J. Chromatogr. 164(4) 416-426 (1979) ... 

The above method, contrary to the methods of estimation of amino acids based on copper complexes, is selective. A threefold excess of several common amino acids (including histamine) does not interfere. The method thus enables free histidine to be determined in protein hydrolysates, provided that the histidine concentration is sufficiently high. Tryptophane deforms the polaro-graphic waves when present in an amount corresponding to half that of histidine (above 1 mg/10 ml.). Mercaptoamino acids also interfere, but most of the types of compounds are destroyed during the protein acidic hydrolysis. Glycine affects the end-point if present in amounts larger than 10 mg/10 ml. of the sample. 

Tables Deposition of collagen-glycosaminoglycan conjugates on poly(octadecen-a/f-maleic anhydride)-coated substrates. Fibrillogenesis and immobilization of fibrillar collagen (1.2 mg/ml) was performed for 2 h at 37 ° C in the presence of heparin and hyaluronic acid (0.4, 1.2 and 5.0 mg/ml, respectively). Thickness of the layers was determined ellip-sometrically using the refractive index of 1.6035 for the dried collagen layer. The collagen amount was determined by amino acid-based HPLC analysis after acidic hydrolysis of surface-bound collagen...

Edsall, J. T. George Scatchard, John G. Kirkwood, and the electrical interactions of amino acids and proteins. Trends Biochem. Sci. 7 (1982) 414-416. Eigen, M. Proton transfer, acid-base catalysis, and enzymatic hydrolysis. Angew. Chem. Int. Ed. Engl. 3 (1964) 1-19. 

Simple esters cannot be allylated with allyl acetates, but the Schiff base 109 derived from o -amino acid esters such as glycine or alanine is allylated with allyl acetate. In this way. the o-allyl-a-amino acid 110 can be prepared after hydrolysis[34]. The Q-allyl-o-aminophosphonate 112 is prepared by allylation of the Schiff base 111 of diethyl aminomethylphosphonates. [35,36]. Asymmetric synthesis in this reaction using the (+ )-A, jV-dicyclohex-ylsulfamoylisobornyl alcohol ester of glycine and DIOP as a chiral ligand achieved 99% ec[72]. 

The differences in the amino acid chemistry of the hide coUagen and the hair keratin are the basis of the lime-sulfide unhairing system. Hair contains the amino acid cystine. This sulfur-containing amino acid cross-links the polypeptide chains of mature hair proteins. In modem production of bovine leathers the quantity of sulfide, as Na2S or NaSH, is normally 2—4% based on the weight of the hides. The lime is essentially an unhmited supply of alkah buffered to pH 12—12.5. The sulfide breaks the polypeptide S—S cross-links by reduction. Unhairing without sulfide may take several days or weeks. The keratin can be easily hydrolyzed once there is a breakdown in the hair fiber stmcture and the hair can be removed mechanically. The coUagen hydrolysis is not affected by the presence of the sulfides (1—4,7). 

Conversion of aniline to acetanilide [103-84-4] by reaction with acetic anhydride, is a convenient method for protecting the amino group. The acetyl group can later be removed by acid or base hydrolysis. 

En me Mechanism. Staphylococcal nuclease (SNase) accelerates the hydrolysis of phosphodiester bonds in nucleic acids (qv) some 10 -fold over the uncatalyzed rate (r93 and references therein). Mutagenesis studies in which Glu43 has been replaced by Asp or Gin have shown Glu to be important for high catalytic activity. The enzyme mechanism is thought to involve base catalysis in which Glu43 acts as a general base and activates a water molecule that attacks the phosphodiester backbone of DNA. To study this mechanistic possibiUty further, Glu was replaced by two unnatural amino acids. 

Much of what is known about the chymotrypsin mechanism is based on studies of the hydrolysis of artificial substrates—simple organic esters, such as /Miitrophenylacetate, and methyl esters of amino acid analogs, such as... 

Definitive identification of lysine as the modified active-site residue has come from radioisotope-labeling studies. NaBH4 reduction of the aldolase Schiff base intermediate formed from C-labeled dihydroxyacetone-P yields an enzyme covalently labeled with C. Acid hydrolysis of the inactivated enzyme liberates a novel C-labeled amino acid, N -dihydroxypropyl-L-lysine. This is the product anticipated from reduction of the Schiff base formed between a lysine residue and the C-labeled dihydroxy-acetone-P. (The phosphate group is lost during acid hydrolysis of the inactivated enzyme.) The use of C labeling in a case such as this facilitates the separation and identification of the telltale amino acid. 

Hydrolyses of aminopyridopyrimidines to the corresponding pyridopyrimidones by means of acid, base, and nitrous acid have been reported. 4-Amino compounds are stable to nitrous acid, but are much more labile than the 2-amino derivatives toward acid- or base-catalyzed hydrolysis. The aminochloro-pyrido[2,3-d]pyrimidine (160) has been converted into the 2,4-dianilino analog (161) by reaction with aniline." ... 

A more general method for preparation ofa-amino acids is the amidotnalmatesynthesis, a straightforward extension of the malonic ester synthesis (Section 22.7). The reaction begins with conversion of diethyl acetamidomalonate into an eno-late ion by treatment with base, followed by S 2 alkylation with a primary alkyl halide. Hydrolysis of both the amide protecting group and the esters occurs when the alkylated product is warmed with aqueous acid, and decarboxylation then takes place to vield an a-amino acid. For example aspartic acid can be prepared from, ethyl bromoacetate, BrCh CCHEt ... 

The Japanese firm Tanabe Inc Ltd has been operating, since 1969, the optical resolution of DL-amino acids using aminoacylase. The prindple is based on the asymmetrical hydrolysis of N-acyl-DL-amino add by amino acylase which gives the L-amino add and the unhydrolysed acyl-D-amino add. 

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