Vertebrates sources

Biogenic amines are decarboxylated derivatives of tyrosine and tryptophan that are found in animals from simple invertebrates to mammals. These compounds are found in neural tissue, where they function as neurotransmitters, and in non-neural tissues, where they have a variety of functions. The enzymes involved in biogenic amine synthesis and many receptors for these compounds have been isolated from both invertebrate and vertebrate sources. In all cases, the individual proteins that effect biogenic amine metabolism and function show striking similarity between species, indicating that these are ancient and well-conserved pathways. 

Unless the last-mentioned product is removed by the inclusion of catalase, the oxoacid is liable to react further, undergoing oxidative decarboxylation to the carboxylic acid. An attractive feature of this group of enzymes in the present context is that there exist readily available representatives of both enantiospecificities. The well-studied and commercially available AAOs from vertebrate sources, such as l-AAO from snake venom and D-AAO from pig kidney, are expensive, however, and are increasingly being replaced by enzymes from microbial sources. 

FIGURE 4.1 Percent identity matrix for tropomyosins from molluscan shellfish, crustacean shellfish, insects and mites, and vertebrate sources. Compiled with the assistance of John C. Wise, Bioinformatics Specialist, University of Nebraska, Food Allergy Research Resource Program. 

The hydroxylation of specific Pro residues in procollagen, the precursor of collagen, requires the action of the enzyme prolyl 4-hydroxylase. This enzyme (Mt 240,000) is an a2/32 tetramer in all vertebrate sources. The proline-hydroxylating activity is found in the a subunits. (Researchers were surprised to find that the )3 subunits are identical to the enzyme protein disulfide isomerase (PDI p. 152) these subunits do not participate in the prolyl hydroxylation activity.) Each a subunit contains one atom of nonheme iron (Fe2+), and the enzyme is one of a class of hydroxylases that require a-ketoglutarate in their reactions. 

Vertebrate source References Total No. of reports noted... 

Calmodulin from Tetrahymena presents interesting contrasts to calmodulins purified from vertebrate sources, and has, for example, 11 amino acid substitutions and one deletion of an amino acid residue compared to bovine brain calmodulin. Most of these variant residues are located near or at the III and IV Ca2+-binding sites. Tetrahymena calmodulin is very specific to... 

Figure 32 (a) Mineral materials found in the statoconia and otoliths of vertebrates (source Nolf, 1985, figure 1, p. 3). 

Again, DFR from vertebrate sources has the residue Tyr-31 in place of the less less bulky Leu-27 of the bacterial enzymes these residues line the pocket in which the pteridine nucleus has to fit in each case. Vertebrate enzymes, which have about 185 residues, are larger than those of bacteria with about 165 residues. How this difference comes about is seen in chicken liver enzyme which has three extra loops on the edge of the pleated sheet, all of them free from normal interchain hydrogen-bonding (Volz etal., 1982). Unlike bacterial DFR, mammalian DFR can reduce folate as well as dihydrofolate. 

X-ray diffraction analysis of dihydrofolate reductase (DHFR), co-crystal-lized with methotrexate, has shed much light on the action of this inhibitor. This work, one of the earliest visualizations of a drug interacting with its receptor (Matthews etal., 1977), has since been refined to the remarkably clear resolution of 1.7 A (Bolin et al., 1982). A typical diagram of DHFR, its coenzyme (NADPH), and methotrexate is shown in Fig. 9.4. The enzyme depicted there is from Lactobacillus casei and the same authors also report on DHFR (with cocrystallized methotrexate) from the bacterium E. colt. However, they have not been able to co-crystallize methotrexate with DHFR from any vertebrate source. 

Whereas the use of synthetic substrates in lieu of native collagen is appropriate in studies with collagenase from clostridial sources, their use in studies of collagenases derived from vertebrate sources cannot be endorsed at this time. The actual amino acid sequence and or other structural requirements that may be recognized by vertebrate collagenases are still unknown. Until these requisites have been determined, we will not know whether splitting of a synthetic substrate represents nonsi)Ccific peptidase activity or specific collagenolytic effect. 

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