دانلود رایگان مقاله انگلیسی سیستم های فرعی: بیوسنتز های NAD و NADP به همراه ترجمه فارسی
|عنوان فارسی مقاله:
|سیستم های فرعی: بیوسنتز های NAD و NADP
|عنوان انگلیسی مقاله:
|Subsystem: NAD and NADP Biosynthesis
|رشته های مرتبط:
|زیست شناسی، علوم سلولی و مولکولی، بیوشیمی، ژنتیک و میکروبیولوژی
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Nicotinamide dinucleotide (NAD) and its phosphorylated analog (NADP) are indispensable co-factors of numerous oxydoreductases in all forms of cellular life. In addition to that, NAD is a co-substrate for a number of other enzymes such as bacterial DNA ligase, various ADP-ribosylating factors, and a few others. NAD-dependent protein deacetylases of CobB/Sir2 family recently attracted much attention due to their perceived role in a number of regulatory processes in eukaryotic cells [1,2]. Biogenesis and maintenance of NAD pool in various species is one of the most important paradigms of metabolic biochemistry.
Although most of the classic biochemical studies related to NAD biosynthesis were performed in 60-80s , many key genes remained unknown until recently. Sequencing and comparative analysis of genomes enabled identification of previously missing genes (for overview see [4,5,6]) and allowed us to project the accumulated knowledge from a handful of model organisms to many others. We have attempted to capture this growing understanding within a framework of the SEED subsystem.
II. Subsystem notes
A table of functional roles (mostly enzymes) directly involved in various aspects of NAD biosynthesis is given in Panel 1. A subsystem diagram reflects the key reactions and pathways leading to the formation of NAD and NADP is presented in Panel 2. Note, that this subsystem in its entirety (including alternative, non-orthologous, forms of enzymes, as defined in Panel 1) is not implemented in any single organism. We have analyzed occurrence of individual functional roles in ~ 300 complete or almost complete genomes included in the current version of the subsystem (available in this release of The SEED).
Among analyzed species, 21 archaea, 13 eukaryotes and the rest are bacteria. This analysis allows to infer the presence or absence of semi-independent modules implemented by sub-sets of roles (see Panel 1 and 2), eg “de novo biosynthesis from aspartate” or “salvage of vitamin B3 via NAM/NAPRT”, etc. We have attempted to capture various combination of such modules and other features (eg alternative forms) using a concept of functional variants assigned with numeric “bar-codes” (see Panel 3 and a series of examples after it). The analysis of distribution of functional variants across a variety of species contributes to understanding of the evolution, physiology and enzymology of NAD biosynthesis. In addition to that, it allows to map open problems (eg missing genes) and to suggest a strategy for their elucidation. A short summary of such problems is provided in Section III.