The molar ratio of RuBP carboxylase/oxygenase to the CF1 complex was determined in the wild type N. tabacum var. JWB and in various N. tabacum mutants, which differ with respect to their chloroplast structure and their photosynthetic and photorcspiratory activity. It appears that the ratio RuBP carboxylase oxygenase, CF1 is not constant in the different mutants, and apparently depends on the chloroplast structure and the photosynthetic capacity. In the green phenotypes of N. tabacum var. Consolation, var. NC 95 and var. Xanthi. whose lamellar system consists of a balanced ratio of grana and intcrgrana regions the ratio is 3-4 RuBP car- boxylase/oxygenase molecules per CF1 complex. In chloroplasts of the yellow-green mutant Su/su, and the yellow mutant of N. tabacum var. Consolation, whose lamellar system consists of extended intergrana regions and low stacked grana the RuBP carboxylase oxygcnasc/CF1 ratio is reduced to about one half. The aurea mutant A. tabacum Susu var. aurea and the yel- low-green leaf patches of variegated tabacum var. Xanthi arc characterized by the fact that one molecule RuBP carboxylase oxygenase correlates to two CF1 complexes. Also in the two N. tabacum mutants Su/su and Consolation green, that exhibit a 30% higher photorespiration these molar ratios depend on the chloroplast structure. The determination of the maximal binding of antibodies out of homologous and non-homo- logous antisera onto RuBP carboxylase oxygenase of the N. tabacum mutant Consolation showed, that the enzyme of the green mutant, which exhibits a higher oxygenase activity, has in comparison to the yellow-green and yellow phenotype of this mutant series and also in comparison to the wild type a 30 per cent higher antibody binding capacity. These differences in antibody binding arc shown in both the region of enzyme antibody equivalence and that of antibody excess. With the methods of enzyme-antibody precipitation in agarose gels these differences of enzymes, exhibiting higher or lower oxygenase activities, cannot be detected. The native enzymes and the large subunits of the enzyme of the three Consolation mutants yield in these test reactions with the enzyme of the wild-type fusing precipitation bands. Treatment with the chemical agent hydroxylamine. as well as heat treatment at 50 °C alters the enzyme conformation to such an extent that the antibody binding capacity is increased by 70%. The difference in the higher antibody binding capacity of the enzyme of the green mutant of N. tabacum var. Consolation is maintained also after these chemical modifications.
Background: Numerous epidemiological studies have demonstrated an association between elevated levels of the endogenous inhibitor of nitric oxide synthases asymmetric dimethylarginine (ADMA) with cardiovascular diseases. ADMA can be hydrolysed by dimethylarginine dimethylaminohydrolase (DDAH). It can also be metabolized through a much less explored alternative pathway by alanine:glyoxylate aminotransferase 2 (AGXT2), which converts ADMA to α-keto-δ-(N,N-dimethylguanidino)valeric acid (ADGV). It has been shown in previous Northern Blot and in-situ RNA-hybridisation experiments that the kidney is the main organ of Agxt2 expression in rats, while RT-PCR and Western Blot studies suggested that Agxt2 is expressed in the mouse kidney and liver at comparable levels. The goal of the current study was to analyse the expression of the enzyme in human tissues. Methods and Results: We performed immunohistochemical staining using two rabbit polyclonal anti-AGXT2 antibodies in both frozen and paraformaldehyde-fixed samples from a normal tissue bank. We saw the strongest expression of AGXT2 using both of the antibodies in the proximal convoluted tubule of the kidney and in the liver with a homogenous pattern throughout all the samples. We also observed weak staining in the skeletal and heart muscle. Aorta, small intestine and lungs were negative for AGXT2 expression. We also confirmed our immunohistochemistry data by RT-PCR. Conclusions: Our current data suggest that both hepatocytes and kidney tubular epithelial cells are the major sources of AGXT2 in humans. We are currently designing experiments to show the direct localization of AGXT2 in a human cell.
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