Redox regulation enzyme regulatory mechanisms

Clearly, the control of gene expression at the transcriptional level is a key regulatory mechanism controlling carotenogenesis in vivo. However, post-transcriptional regulation of carotenoid biosynthesis enzymes has been found in chromoplasts of the daffodil. The enzymes phytoene synthase (PSY) and phytoene desaturase (PDS) are inactive in the soluble fraction of the plastid, but are active when membrane-bound (Al-Babili et al, 1996 Schledz et al, 1996). The presence of inactive proteins indicates that a post-translational regulation mechanism is present and is linked to the redox state of the membrane-bound electron acceptors. In addition, substrate specificity of the P- and e-lycopene cyclases may control the proportions of the p, P and P, e carotenoids in plants (Cunningham et al, 1996). 

A different control mechanism results from allosteric interactions between distinct sites this is a central regulatory mechanism employed by proteins. While there are numerous examples of allosteric control of the activity of enzymes, receptors, and transport proteins, regulation of ET in redox enzymes has rarely been documented, and no kinetic analysis of such processes has been performed. Interestingly, site-site interactions involved in control of electron... 

Based on the general hypothesis—the interconversions of proline, ornithine and glutamate regulate the NADF " - NADPH redox state — one can reexamine the diverse regulatory mechanisms regulating this enzyme system relative to a metabolic endpoint other than the exchange... 

Apart from being a cofactor of prolyl and lysyl hydroxylase, ascorbate affects the hydroxylation of procollagen at various levels of regulation. It activates a silent form of prolyl hydroxylase (Mussini et al., 1961 Stassen et al, 1973 Hayaishi et al, 1975 Cardinale et al, 1975) and may also increase the enzyme levels by transcriptional activation and translational events (Qian et al, 1993). Interestingly, all these regulatory interventions appear to be linked to the redox properties, i.e., the prooxidant potential of ascorbate. The activation of the inactive form of prolyl hydroxylase is reversed by dithiothreitol (Hayaishi et al, 1975) and the induction of its biosynthesis appears to be mediated by the superoxide ion, which activates an epigenetic control mechanism involving poly ADP-ribose the induction of prolyl hydroxylase by ascorbate is prevented by both addition of superoxide dismutase and inhibition of poly ADP-ribose synthetase (Qian et al, 1993). 

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