Mouse brain enzyme

The presence of o-serine in mammalian brain tissue was first reported in 1989 [33, 34]. It has recently been established that o-serine is employed in the mammalian forebrain as a co-agonist for the N-methyl-o-asparate (NMDA) excitatory amino acid receptor [35, 36]. A PLP-dependent serine racemase has been cloned and purified from mammalian brain, and found to be a homodimer, which has a number of nonessential cofactors that enhance its activity, including Ca +, Mg + and ATP [37-40]. The mouse brain enzyme has also been shown to catalyze elimination from L-serine, to form pyruvate, with an activity comparable to that for racemiza-tion [41]. Interestingly, the first instance of this class of racemase was discovered by Esaki and coworkers in the silkworm, Bombyx mori [42]. o-serine concentration in the blood of B. mori larvae is thought to play a role in metamorphosis. 

FAAH was originally purified and cloned from rat liver microsomes and is able to catalyse the hydrolysis of anandamide and 2-AG, in addition to other long-chain fatty acid amides [25]. Studies into the structure and role of this enzyme have generated interest in the potential therapeutic applications of FAAH inhibitors [26-28]. FAAH knock-out mouse brains contained 15-fold higher levels of anandamide than their wild-type counterparts and these animals have also been shown to be more responsive to exogenously administered anandamide [29]. These animals also showed a reduced response to painful stimuli, supporting the hypothesis that FAAH inhibition may provide novel analgesics. Levels of 2-AG were not elevated in the FAAH knock-out animals, apparently due to the existence of alternative metabolic fates for this compound [30]. 

The temporal appearance of myelin-related lipids and enzymes in the cultures of dissociated fetal mouse brain cells mimics the temporal development of these parameters in normal mouse or rat brain (12, 5, 29, 28). The types of myelin-related lipids and the order of magnitude of the activities of the enzymes producing some of these lipids are the same as those found in brain in vivo (30, 29, 28). 

The apparent Km values of the enzyme systems for CMP-NeuNAc assayed with 0.5 mg enzyme protein, was 0.13 mM (same with all four types of acceptors (15)). This value is comparable to that (0.15 mM) obtained (22) in cultured mouse neuroblastoma cells with lactosylceramide as the NeuNAc acceptor. The Km value reported previously (23) for the calf brain enzyme with desialy-lated ai-acid glycoprotein as the acceptor is 4-fold higher. 

The enzymic oxidative deamination of simple phenethylamines is exemplified by the reported bio transformations of mescaline (146) (114, 115) and ephedrine (148) (116). Mescaline is metabolized to 3,4,5-trimethoxy-phenylacetic acid by tissue homogenates of mouse brain, liver, kidney, and heart (114,115). 3,4,5-Trimethoxybenzoic acid is also formed as a minor metabolite. The formation of jV-acetylmescaline (147), a significant metabolite in vivo, was not observed in the in vitro studies. Both D-(—)-and L-(+)-ephedrine have been incubated with enzyme preparations from rabbit liver norephedrine (149), benzoic acid, and 1-phenyl-1,2-propanediol were characterized as metabolites (116). The D-(—)-isomer was the better substrate, being more rapidly converted. Similar results were previously reported with rabbit liver slices as the source of enzyme (153,154). The enzymic degradation of the side chain of /i-phenethylamines has been extensively investigated with nonalkaloid substrates such as amphetamine (151) and jV-methylamphetamine (150) (10,155-157), and the reader is referred to these studies for a more comprehensive coverage of this aspect of the subject. 

Primary cultured porcine or bovine brain capillary endothelial cells have been used as an in vitro model for the BBB. Recently, an immortalized cell line has been established from mouse, rat, and human brain capillary endothelial cells by infection with Simian virus 40 or transfection of SV40 large T antigen (45 -7). Tatsuta et al. established an immortalized mouse brain capillary endothelial cell line (MBEC4). The activity of y-glutamyl transpeptidase and alkaline phosphatase, specific marker enzymes for brain capillary endothelial cells, was half that in the brain capillary (45). Also, P-gp was expressed on the apical membrane of MBEC4 cells, which corresponds to the abluminal membrane of the brain... 

Duan et al. reported the use of a rapid and simple method for the determination of acetylcholine and choline in mouse brain by high performance liquid chromatography, making use of an enzyme-loaded post column and an electrochemical detector [144]. Perchloric acid extracts of small brain tissue were injected onto the HPLC system with no prior clean-up procedure. Detection limits for both compounds were 1 pmol, and this method was successfully applied to the measurement of acetylcholine in discrete brain areas of the mouse. 

Eicompak AC-GEL 0.07 M-Phosphate buffer containing 60 ppm of Na2 EDTA, 0.065% of tetramethyl ammonium chloride and 0.3 of sodium octane-sulfonate Electrochemical Mouse brain tissues. An immobilized enzyme column with ChO and AChE was used. [172]... 

The enzyme was prepared from mouse brain homogenized in phosphate buffer. An S-100 solution was prepared and used as the source of the synthetase. 

Serine Racemase (EC 5.1.1.16] Serine racemases have been discovered in both bacteria and eukaryotes (for a review see [60, 62). In the latter organisms, serine racemase catalyzing the conversion of L-Ser to D-Ser was at first discovered in the silkworm Bombyx mori it is a PLP-dependent racemase which is also active on L-Ala (-6% of the activity on L-Ser). A serine racemase was also purified from rat brain (and a serine racemase cDNA was cloned from mouse brain). Mammalian serine racemase shows sequence simUarily with L-threonine dehydratase from various sources all the active site residues of the latter enzyme are also conserved in mouse serine racemase. Mammalian serine racemase is a member of the fold-type II group of PLP enzymes (similarly to L-threonine dehydratase, D-serine dehydratase, and so on) and distinct from alanine racemase, which belongs to the fold-type III group. Mouse serine racemase shows a low kinetic efficiency the Km values for L- and D-Ser are -10 and 60 mM, respectively and the V ax values with L- and D-Ser are 0.08 and 0.37 units/mg protein (less than 0.1% of those of alanine racemase on L- and D-Ala, see above). 

Mizuno Y, Sone N, Saitoh T (1987) Effects of l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine and l-methyl-4-phenylpyiidinium ion on activities of the enzymes in the electron transport system in mouse brain. J Neurochem 48 1787-1793... 

Apelt J, Ach K, Schliebs R (2003) Aging-related down-regulation of neprilysin, a putative beta-amyloid-degrading enzyme, in transgenic Tg2576 Alzheimer-like mouse brain is accompanied by an astroglial upregulafion in the vicinity of beta-amyloid plaques. Neurosci Lett 339 183—186. 

Cystathionine is the first intermediate metabolite in transsulfuration, formed from HCY and serine by cystathionine-fi-synthase, a redox-sensitive, heme-containing enzyme (Banerjee et al., 2003), whose activity is lower in males vs. females (Vitvitsky et al., 2007). The higher levels of cystathionine in human brain reflect a strong diversion of HCY to transsulfuration (i.e., low methionine synthase activity and high cystathionine-f)-synthase activity), in conjunction with a decreased conversion of cystathionine to cysteine. As illustrated in Fig. 1, this indicates impaired transsulfuration in human brain. Low transsulfuration activity relative to other tissues has been described in rat or mouse brain (Finkelstein, 1990), although a... 

Following along these lines Yamamoto e al. (89) examined the effects of chronic morphine treatment on the Mg -dependent ATPase of synaptic vesicles. Since this enzyme has been implicated in the regulation of neurotransmitter release (90,91), it appears a likely enzyme candidate to be altered by opiates. Consistent with this anticipation, it was found that the activity of Mg dependent ATPase in mouse brain synaptic vesicles was significantly increased with tolerance development while that of the Mg 2+ dependent ATPase and Na+, K" activated ATPase from SPM fractions were not altered. Kendrick t al. (92) have shown that Mg +-ATPase may be involved in the accumulation of Ca + by synaptic vesicles the increased Ca2+ content of vesicles seen in tolerant animals could thus arise from increased enzymatic activity. Such a homeostatic mechanism would serve to overcome reduced levels of neurotransmitter release due to the opiate. 

Sadasivudu B, Murthy RK. 1978. Effects of ammonia on monoamine oxidase and enzymes of gaba metabolism in mouse brain. Arch Int Physiol Biochim 86 67-82. 

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