Biosynthesis Brain tissue

Nonphysiological compounds have also been described as influencing the overall metabolism of sialic acid. Administration of ethanol (2 g/kg) to rats significantly decreases the sialic acid content of brain tissue.246 Convulsions induced by pentylenetetrazole (6,7,8,9-tetrahy-dro-5/f-tetrazoloazepine) are accompanied by a diminution in the rate of biosynthesis of polysialogangliosicles GT, and GQn, in rat brain.227 Such ManNAc analogs as 2-acetamido-l,3,4,6-tetra-0-acetyl-2-deoxy-D-mannopyranose or the 2-(trifluoroacetamido) derivative lead to a marked lowering of the incorporation of radioactivity from labelled ManNAc into glycoconjugate sialic acids of murine, erythroleukemia (Friend) cells.247... 

GlcT (UDP-glucose A-acylsphingosine D-glucosyltransferase) transfers glucose from UDP-Glc to ceramide in brain tissues, which is the first step in biosynthesis of the major gangliosides except GM4 (O Fig. 1). The cDNA of GlcT has been cloned from human [96], mouse [97], and... 

Very little is known about the biosynthesis of the three most recently proposed endocannabinoids, 2-AGE, virodhamine and NADA. Regarding 2-AGE (noladin ether), this compound was previously identified in pig brain (Hanus et al. 2001) and in some rat tissues and brain areas (Fezza et al. 2002) by using mass-spectrometric (MS) methods coupled to chromatographic separations. However, a recent study cast some doubt on the actual existence of 2-AGE in mammalian brain tissue (Oka et al. 2003). At the time of this study it was already known that (1) the only acyl ethers to have been detected in animals before the discovery of 2-AGE were 2-acyl ethers (e.g. alkenyl ethers such as platelet activating factor and plasmalogens) (2) there was no evidence for the existence of any enzyme catalysing the formation... 

Glutamine synthetase catalyzes the ATP-dependent biosynthesis of glutamine according to equation (1). This enzyme plays a central role in nitrogen metabolism. In mammalian brain tissue, glutamine synthetase converts the neurotransmitter glutamate into glutamine. 

This reaction is analogous to that previously described for the biosynthesis of choline plasmalogen (Reaction 17). It also occurs in brain tissue (McMurray 1964b). 

Decarboxylases function in the synthesis of major neurotransmitters (26) adequate PLP supply in brain tissue is therefore essential for normal brain function. Aminotransferases have a key function in both amino acid biosynthesis and catabolism. PLP has also a structural function (27) in glycogen phosphorylase (EC 2.4.1.1), and a role for PLP in lipid metabolism has been proposed (28,29). 

It is interesting that H and C are incorporated from L-[methyl- H, C]-methionine into cholesterol and 5a-cholest-7-en-3P-ol in normal and tumorous rats. The exact mechanism of this incorporation is obscure at present. There has been an increased interest in the biosynthesis and metabolism of cholesterol in brain tissue. This area has also been reviewed recently. The primary pathway of sterol biosynthesis in adult rat brain seems to be via A -intermediates. It is interesting that the conversion of squalene into sterols by microsomal fractions from brains of immature rats requires the lOOCKX) X g supernatant fraction from liver, the corresponding supernatant fraction from brain being inactive. ... 

How is NAPE synthesized, and how is its biosynthesis controlled Unfortunately, we cannot satisfactorily answer this question at present. A calcium-dependent enzyme activity that catalyzes the transfer of fatty acyl groups from various donor phospholipids to PE, producing NAPE, has been partially characterized in dog brain tissue and in primary cultures of rat brain neurons.In these neurons, NAPE biosynthesis is stimulated by stimuli that elevate intracellular calcium levels and is potentiated by cAMP-dependent protein kinase activity. But the physiological roles, anatomical distribution and regulation of NAPE biosynthesis in the adult nervous system remain unknown. 

Basu, M., Hawes, J. W., Li, Z., Ghosh, S., Khan, F. A., Zhang, B. J., and Basu, S., 1991, Biosynthesis in vitro of SA-Le and SA-diLe by al-3fucosyltransferases from colon carcinoma cells and embryonic brain tissues, Glycobiology 1 527-535. 

Cumar, F. A., TaUman, J. F., and Brady, R. O., 1972, The biosynthesis of a disialylgan-glioside by galactosyltransferase from rat brain tissue, J. Biol. Chem. lAlxiyil. 

L-Tyrosine metabohsm and catecholamine biosynthesis occur largely in the brain, central nervous tissue, and endocrine system, which have large pools of L-ascorbic acid (128). Catecholamine, a neurotransmitter, is the precursor in the formation of dopamine, which is converted to noradrenaline and adrenaline. The precise role of ascorbic acid has not been completely understood. Ascorbic acid has important biochemical functions with various hydroxylase enzymes in steroid, dmg, andhpid metabohsm. The cytochrome P-450 oxidase catalyzes the conversion of cholesterol to bUe acids and the detoxification process of aromatic dmgs and other xenobiotics, eg, carcinogens, poUutants, and pesticides, in the body (129). The effects of L-ascorbic acid on histamine metabohsm related to scurvy and anaphylactic shock have been investigated (130). Another ceUular reaction involving ascorbic acid is the conversion of folate to tetrahydrofolate. Ascorbic acid has many biochemical functions which affect the immune system of the body (131). 

Glycosydation AChE and BChE carry 3 and 9, respectively, N-glycosylation consensus sequences attaching carbohydrate residues to the core protein via asparagines. Different molecular forms of the enzymes in various tissues, show different number and composition of carbohydrate residues. N-glycosylation at all sites was shown to be important for effective biosynthesis, secretion and clearance of ChEs from the circulation. Altered patterns of AChE glycosylation have been observed in the brain and cerebrospinal fluid of Alzheimer s disease (AD) patients, with potential diagnostic value. 

Liver, the major site of purine nucleotide biosynthesis, provides purines and purine nucleosides for salvage and utilization by tissues incapable of their biosynthesis. For example, human brain has a low level of PRPP amidotransferase (reaction 2, Figure 34-2) and hence depends in part on exogenous purines. Erythrocytes and polymorphonuclear leukocytes cannot synthesize 5-phosphoribosylamine (strucmre III, Figure 34-2)... 

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