China
Africa
Explore chapters and articles related to this topic
Biochemical Effects in Animals
Published in Stephen P. Coburn, The Chemistry and Metabolism of 4′-Deoxypyridoxine, 2018
Goryachenkova et al.171 compared cystathionine-beta-synthase (formerly serine sulfhydrase E.C. 4.2.1.22) and cystathionine-gamma-lyase (E.C. 4.4.1.1, formerly gamma-cystathionase 4.2.1.15). For cystathionine-beta-synthase, inhibition was determined after preincubating the apoenzyme simultaneously with the analog (10−4 JVf) and pyridoxal phosphate (10−5M). For cystathionine-gamma-lyase the concentrations were 2.5 × 10−5 Mand 10−6 M for the analog and cofactor, respectively. 3-Deoxypyridoxal phosphate did not affect the lyase but produced 33% (K, = 4.5 × 10−4M) inhibition of the synthase. Again there was no evidence of formation of an aldimine linkage. 5′-Deoxypyridoxal inhibited both the lyase (24% K, = 9.1 × 10-5) and the synthase (30%, K, = 1.2 × 10−3). 4′-Deoxypyridoxine phosphate was not tested.
Homocysteine: A Risk Factor for Atherothrombotic Cardiovascular Disease
Published in P. K. Shah, Risk Factors in Coronary Artery Disease, 2006
Mathew J Price, Andrew A Zadeh, Sanjay Kaul
Homocysteine is a sulfur amino acid formed during the metabolism of methionine, an essential amino acid that is found in dietary protein. Homocysteine is metabolized by remethylation or transsulfuration (Fig. 1) (1). Remethylation is a salvage pathway; homocysteine acquires a methyl group from 5-methyl-tetrahydrofolate to form methionine in a reaction catalyzed by the vitamin B12-dependent enzyme, methionine synthase. 5-methyl-tetrahydrofolate is derived from folate in a cycle catalyzed by methylene tetrahydrofolate reductase (MTHFR). An alternative pathway for remethylation occurs in the liver, where betaine acts as the methyl donor. Transsulfuration occurs during times of methionine excess or cysteine depletion. Homocysteine combines with serine to form cystathionine via a rate-limiting reaction catalyzed by the B6-dependent enzyme, cystathionine-beta-synthase. Cystathionine-gamma-lyase, another B6-dependent enzyme, then catalyzes the hydrolysis of cystathionine to cysteine, which is then further metabolized to glutathione or sulfate (2).
Water-soluble vitamin insufficiency, deficiency and supplementation in children and adolescents with a psychiatric disorder: a systematic review and meta-analysis
Published in Nutritional Neuroscience, 2023
Nuria Prades, Eva Varela, Itziar Flamarique, Ramon Deulofeu, Inmaculada Baeza
Some of the results mentioned above seem to suggest that an alteration of one-carbon metabolism could be implicated in ASD pathogeny through three interdependent pathways: the folate cycle, the methionine cycle (where methionine is transmethylated depending on folate) and transsulfuration, (which helps synthesize glutathione) [82]. Vitamin B12 also participates in these loop reactions as a cofactor of the enzyme methionine synthase both in the folate and the methionine cycles [83]. Homocysteine is a toxic amino acid that could be produced in excess during abnormal methylation processes [83]. The role of vitamin B6 is to act as a cofactor of the enzymes cystathionine beta synthase and cystathionine gamma lyase in the transsulfuration pathway of homocysteine to cysteine [82]. The one-carbon cycle is key in different functions such as DNA synthesis, epigenetic control of gene expression and, membrane signalling, maintenance of cellular redox homeostasis and detoxification capacity [82]. Apart from that possible biochemical dysfunction, the implication of folate and vitamin B12 insufficiencies in disrupting myelinization and inflammation processes has also been described [84]. All of this makes it clear that the roles of folic acid, vitamin B12 and even vitamin B6 need to be further studied to increase our understanding of their possible relationship with the pathophysiology of ASD. Also, the links between vitamin insufficiency and specific life stages (pregnancy [85]; infancy and childhood [83], or adolescence [83]) should be a focus of future study.
Progress in research on the roles of TGR5 receptor in liver diseases
Published in Scandinavian Journal of Gastroenterology, 2021
Ke Ma, Dan Tang, Chang Yu, Lijin Zhao
Portal hypertension is one of the most important complications of chronic liver disease caused by increased intrahepatic vascular resistance in hepatic fibrosis, microvascular thrombosis, hepatic sinusoid endothelial cell dysfunction, HSC activation, and platelet dysfunction [13]. The manifestations of limbal epithelial stem cell (LESC) dysfunction include decreased permeability and decreased nitric oxide (NO) secretion. In the physiological state, LESCs have high permeability, whereas in chronic liver disease, liver fibrosis causes LESCs to lose fenestration and form a basement membrane, causing a decrease in permeability. As an important vasodilator, a decrease in NO secretion significantly increases intravascular pressure. Notably, TGR5 is highly expressed in LSECs. When TGR5 is activated, it induces the expression and activation of endothelial nitric oxide synthase (eNOS) in endothelial cells, and NO secretion mainly depends on the activity and expression of eNOS [107]. In addition, the activation of TGR5 can trigger the expression of cystathionine-gamma-lyase (CSE) and the serine phosphorylation of eNOS, leading to the production of hydrogen sulphide (H2S) and NO, respectively. Consequently, this inhibits the expression and secretion of the strong vasoconstrictor ET-1 in LSECs (Figure 2) [107–111].
Predicting the functional and structural consequences of nsSNPs in human methionine synthase gene using computational tools
Published in Systems Biology in Reproductive Medicine, 2019
Mansi Desai, Jenabhai B. Chauhan
STRING database was used for the prediction of functional interaction between the methionine synthase and other proteins in the cell. STRING results predicted the functional association of methionine synthase protein with AHCY (adenosylhomocysteinase), CBS (cystathionine beta synthase), CTH (cystathionine gamma lyase), MAT1A (methionine adenosyltransferase I), MAT2A (methionine adenosyltransferase II), MTHFD1 (methylene tetrahydrofolate dehydrogenase I), MTHFD1L (methylene tetrahydrofolate dehydrogenase I like), MTHFR (methylene tetrahydrofolate reductase), MTRR (5-methyl tetrahydrofolate-homocysteine methyl transferase reductase or MSR: methionine synthase reductase) and SHMT1 (serine hydroxymethyltransferase I) (Figure 7).