Enzymes and amino acids

Basic technology for membrane separation of biomolecules was invented in the United States, but the West Germans and the Japanese lead in its application to separations of enzymes and amino acids from complex mixtures. Japanese... 

T. C. Stadtman, Specific occurrence of selenium in enzymes and amino acid tRNAs, FASEB, 1 (1987), 375-379. 

It is also of interest that the decarboxylation of lysine and tyrosine by bacterial enzymes has been shown to be reversible > °. In a reaction mixture consisting of enzyme, and amino acid or amine the was... 

Amino acid metabolism requires the participation of three important cofactors. Pyridoxal phosphate is the quintessential coenzyme of amino acid metabolism (see Chapter 38). All amino acid reactions requiring pyridoxal phosphate occur with the amino group of the amino acid covalently bound to the aldehyde carbon of the coenzyme (Fig. 39.3). The pyridoxal phosphate then pulls electrons away from the bonds around the a-carbon. The result is transamination, deamination, decarboxylation, P-elimination, racemization, and -elimination, depending on which enzyme and amino acid are involved. 

I. D. Ivanov, Polarography of Proteins, Enzymes, and Amino Acids, USSR Academy of Sciences Publishing House, Moscow (1961). In Russian. 

One of the areas selected by the EC is the area of biobased products. The Biobased Products LMI covers a broad range of intermediate products, product components and ready-made products, e.g., bioplastics, biolubricants, biofibres for textiles, composite materials for construction and automotive, chemical building blocks, enzymes and amino acids (see Table 18.1). 

Ion-exchange chromatography has a wide variety of applications including the separation of proteins, hormones, enzymes and amino acids. 

Broadbent, J.R., Cai, H., Larsen, R.L., et al. (2011) Genetic divarsity in proteolytic enzymes and amino acid metabo-hsm among Lactobacillus helveticus strains. J Dairy Sci 94, 4313-4328. 

CCK is found in the digestive tract and the central and peripheral nervous systems. In the brain, CCK coexists with DA. In the peripheral nervous system, the two principal physiological actions of CCK are stimulation of gaU. bladder contraction and pancreatic enzyme secretion. CCK also stimulates glucose and amino acid transport, protein and DNA synthesis, and pancreatic hormone secretion. In the CNS, CCK induces hypothermia, analgesia, hyperglycemia, stimulation of pituitary hormone release, and a decrease in exploratory behavior. The CCK family of neuropeptides has been impHcated in anxiety and panic disorders, psychoses, satiety, and gastric acid and pancreatic enzyme secretions. 

Resolution of Racemic Amines and Amino Acids. Acylases (EC3.5.1.14) are the most commonly used enzymes for the resolution of amino acids. Porcine kidney acylase (PKA) and the fungaly3.spet i//us acylase (AA) are commercially available, inexpensive, and stable. They have broad substrate specificity and hydrolyze a wide spectmm of natural and unnatural A/-acyl amino acids, with exceptionally high enantioselectivity in almost all cases. Moreover, theU enantioselectivity is exceptionally good with most substrates. A general paper on this subject has been pubUshed (106) in which the resolution of over 50 A/-acyl amino acids and analogues is described. Also reported are the stabiUties of the enzymes and the effect of different acyl groups on the rate and selectivity of enzymatic hydrolysis. Some of the substrates that are easily resolved on 10—100 g scale are presented in Figure 4 (106). Lipases are also used for the resolution of A/-acylated amino acids but the rates and optical purities are usually low (107). 

The a/p-barrel structure is one of the largest and most regular of all domain structures, comprising about 250 amino acids. It has so far been found in more than 20 different proteins, with completely different amino acid sequences and different functions. They are all enzymes that are modeled on this common scaffold of eight parallel p strands surrounded by eight a helices. They all have their active sites in very similar positions, at the bottom of a funnel-shaped pocket created by the loops that connect the carboxy end of the p strands with the amino end of the a helices. The specific enzymatic activity is, in each case, determined by the lengths and amino acid sequences of these loop regions which do not contribute to the stability of the fold. 

Most of the known antiparallel p structures, including the immunoglobulins and a number of different enzymes, have barrels that comprise at least one Greek key motif. An example is 7 crystallin, which has two consecutive Greek key motifs in each of two barrel domains. These four motifs are homologous in terms of both their three-dimensional structure and amino acid sequence and are thus evolutionarily related. 

Mitochondria Mitochondria are organelles surrounded by two membranes that differ markedly in their protein and lipid composition. The inner membrane and its interior volume, the matrix, contain many important enzymes of energy metabolism. Mitochondria are about the size of bacteria, 1 fim. Cells contain hundreds of mitochondria, which collectively occupy about one-fifth of the cell volume. Mitochondria are the power plants of eukaryotic cells where carbohydrates, fats, and amino acids are oxidized to CO9 and H9O. The energy released is trapped as high-energy phosphate bonds in ATR... 

Proteins are the indispensable agents of biological function, and amino acids are the building blocks of proteins. The stunning diversity of the thousands of proteins found in nature arises from the intrinsic properties of only 20 commonly occurring amino acids. These features include (1) the capacity to polymerize, (2) novel acid-base properties, (3) varied structure and chemical functionality in the amino acid side chains, and (4) chirality. This chapter describes each of these properties, laying a foundation for discussions of protein structure (Chapters 5 and 6), enzyme function (Chapters 14-16), and many other subjects in later chapters. 

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... 

It is likely that the madurastatins are biosynthesized on a nonribosomal peptide synthetase, from salicylic acid as the starter acid. L-Serine is probably the precursor to the aziridine moiety, with epimerization occurring on the enzyme-bound amino acid as found for other nonribosomal peptides, with aziridine formation occurring at a late stage. Compounds 120 and 123 could therefore be biosynthetic precursors to 119 and 122, respectively. 

The synthesis and metabolism of trace amines and monoamine neurotransmitters largely overlap [1]. The trace amines PEA, TYR and TRP are synthesized in neurons by decarboxylation of precursor amino acids through the enzyme aromatic amino acid decarboxylase (AADC). OCT is derived from TYR. by involvement of the enzyme dopamine (3-hydroxylase (Fig. 1 DBH). The catabolism of trace amines occurs in both glia and neurons and is predominantly mediated by monoamine oxidases (MAO-A and -B). While TYR., TRP and OCT show approximately equal affinities toward MAO-A and MAO-B, PEA serves as preferred substrate for MAO-B. The metabolites phenylacetic acid (PEA), hydroxyphenylacetic acid (TYR.), hydroxymandelic acid (OCT), and indole-3-acetic (TRP) are believed to be pharmacologically inactive. 

Sulfite reductase catalyzes the six-electron reduction of sulfite to sulfide, m essential enzymatic reaction in the dissimilatory sulfate reduction process. Several different types of dissimilatory sulfite reductases were already isolated from sulfate reducers, namely desul-foviridin (148-150), desulforubidin (151, 152), P-582 (153, 154), and desulfofuscidin (155). In addition to these four enzymes, an assimila-tory-type sulfite reductase was also isolated from D. vulgaris. Although all these enzymes have significantly different subunit composition and amino acid sequences, it is interesting to note that, as will be discussed later, all of them share a unique type of cofactor. 

The central role of the mitochondrion is immediately apparent, since it acts as the focus of carbohydrate, hpid, and amino acid metabohsm. It contains the enzymes of the citric acid cycle, P-oxidation of fatty acids, and ketogenesis, as well as the respiratory chain and ATP synthase. 

These include the mitochondrial respiratory chain, key enzymes in fatty acid and amino acid oxidation, and the citric acid cycle. Reoxidation of the reduced flavin in oxygenases and mixed-function oxidases proceeds by way of formation of the flavin radical and flavin hydroperoxide, with the intermediate generation of superoxide and perhydroxyl radicals and hydrogen peroxide. Because of this, flavin oxidases make a significant contribution to the total oxidant stress of the body. 

Pantothenic acid is present in coenzyme A and acyl carrier protein, which act as carriers for acyl groups in metabolic reactions. Pyridoxine, as pyridoxal phosphate, is the coenzyme for several enzymes of amino acid metabolism, including the aminotransferases, and of glycogen phosphorylase. Biotin is the coenzyme for several carboxylase enzymes. 

Since the modification that causes loss of activity in the enzyme H- K 234 does not interfere with the formation of the PG-PGIP complex, the site re onable for PGIP recognition may redde in a domain different fiom the active e. Studies are now under way to establish wdiich e(s) and amino acid residues of the e/uiiopolygalacturonase are critical for interaction with PGIP. 

With the death of the bean, cellular structure is lost, allowing the mixing of water-soluble components that normally would not come into contact with each other. The complex chemistry that occurs during fermentation is not fully understood, but certain cocoa enzymes such as glycosidase, protease, and polyphenol oxidase are active. In general, proteins are hydrolyzed to smaller proteins and amino acids, complex glycosides are split, polyphenols are partially transformed, sugars are hydrolyzed, volatile acids are formed, and purine alkaloids diffuse into the bean shell. The chemical composition of both unfermented and fermented cocoa beans is compared in Table 1. 

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