In silico assessment of gene function involved in cysteine biosynthesis in Arabidopsis: expression analysis of multiple isoforms of serine acetyltransferase.

In plants, the inorganic sulfur is first fixed into cysteine by the cysteine biosynthetic pathway. This biosynthetic pathway of cysteine involves several enzymatic reactions. In Arabidopsis thaliana, multiple isoforms seem to participate in each enzymatic step for cysteine biosynthesis. To obtain more insights on the specific role of each isoform involved in the cysteine biosynthesis, in silico analysis of these isoforms using Arabidopsis expressed sequence tags (EST) database was carried out. This EST database analysis revealed distinct population distribution of ESTs among multiple isoforms, suggesting that each isoform has its particular expression pattern, presumably associated with its specific role in cysteine biosynthesis. As another in silico analysis, co-expression analysis of genes involved in sulfur metabolism in Arabidopsis was performed using a public transcriptome database of DNA microarrays. This co-expression analysis also suggested specific function and co-regulation of some isoform genes for cysteine biosynthesis by consideration on the clustering of co-expressed genes. From the results of sensitivity to feedback regulation, subcellular localization and expression of mRNA analyses, each serine acetyltransferase (SATase) isoform seems to have its specific role for cysteine biosynthesis. Similar expression patterns were observed between the experimental results of expression data for SATase isoforms and the in silico results of "digital northern" analysis using EST database.

Assessment of cysteine synthesis in very low-birth weight neonates using a [13C6]glucose tracer.

BACKGROUND/PURPOSE: Cysteine is an amino acid necessary for the synthesis of all proteins, the antioxidant glutathione, and the neuromodulator taurine. Whether cysteine is an essential amino acid for premature neonates remains controversial. Using a [13C6]glucose precursor in very-low-birth weight (VLBW) premature neonates, we measured the 13C content of cysteine in hepatically derived apolipoprotein (apo) B-100 and in the plasma to determine whether cysteine synthesis occurs and to relate minimum synthetic capacity to neonatal maturity. METHODS: Twelve VLBW premature neonates (birth weight, 907 +/- 274 [SD] g; gestational age, 26.8 +/- 2.4 weeks) were studied on day of life 7.8 +/- 4.2 while on total parenteral nutrition (TPN) for 5.6 +/- 4.5 days. A 4-hour intravenous infusion of [13C6]glucose was administered. Blood samples were obtained immediately before and at the end of the infusion. Isotopic enrichment of cysteine was determined by gas chromatography/mass spectrometry. Analysis of variance, Student's t test, and linear regression were used for comparisons. RESULTS: The 13C isotope ratio of apo B-100-derived cysteine after the [13C6]glucose infusion was significantly higher than baseline (18.57 +/- 0.38 [SEM] vs 17.54 +/- 0.25 mol%, P < .05). The 13C isotope ratio of plasma cysteine was also significantly higher than baseline (17.36 +/- 0.25 vs 16.91 +/- 0.16 mol%, P < .05). When expressed as a product/precursor ratio, the mole percent above baseline of [13C]apo B-100 cysteine/[13C6]glucose correlated with birth weight (r = 0.74, P < .01). CONCLUSIONS: Very low-birth weight neonates are capable of cysteine synthesis as evidenced by incorporation of 13C label into hepatically derived apo B-100 cysteine and plasma cysteine from a glucose precursor. The minimum capacity for intrahepatic cysteine synthesis appears to be directly proportional to the maturity of the neonate and may impact the capabilities of VLBW neonates to counteract oxidative stresses such as bronchopulmonary dysplasia and necrotizing enterocolitis.