Proses biosintesis steroid

Biosynthesis of cholesterol is directly regulated by the cholesterol levels present, though the homeostatic mechanisms involved are only partly understood. A higher intake from food leads to a net decrease in endogenous production, whereas lower intake from food has the opposite effect. The main regulatory mechanism is the sensing of intracellular cholesterol in the endoplasmic reticulum by the protein SREBP (sterol regulatory element-binding protein 1 and 2). In the presence of cholesterol, SREBP is bound to two other proteins: SCAP (SREBP-cleavage-activating protein) and Insig1. When cholesterol levels fall, Insig-1 dissociates from the SREBP-SCAP complex, allowing the complex to migrate to the Golgi apparatus, where SREBP is cleaved by S1P and S2P (site-1 and -2 protease), two enzymes that are activated by SCAP when cholesterol levels are low. The cleaved SREBP then migrates to the nucleus and acts as a transcription factor to bind to the SRE (sterol regulatory element), which stimulates the transcription of many genes. Among these are the low-density lipoprotein (LDL) receptor and HMG-CoA reductase. The former scavenges circulating LDL from the bloodstream, whereas HMG-CoA reductase leads to an increase of endogenous production of cholesterol. A large part of this signaling pathway was clarified by Dr. Michael S. Brown and Dr. Joseph L. Goldstein in the 1970s. In 1985, they received the Nobel Prize in Physiology or Medicine for their work. Their subsequent work shows how the SREBP pathway regulates expression of many genes that control lipid formation and metabolism and body fuel allocation. Cholesterol synthesis can be turned off when cholesterol levels are high, as well. HMG CoA reductase contains both a cytosolic domain (responsible for its catalytic function) and a membrane domain. The membrane domain functions to sense signals for its degradation. Increasing concentrations of cholesterol (and other sterols) cause a change in this domain's oligomerization state, which makes it more susceptible to destruction by the proteosome. This enzyme's activity can also be reduced by phosphorylation by an AMP-activated protein kinase. Because this kinase is activated by AMP, which is produced when ATP is hydrolyzed, it follows that cholesterol synthesis is halted when ATP levels are low [5] .

Peculiarities of synthesis of surface-active substances (SAS) are studied at periodical cultivation of Rhodococcus erythropolis EK-1 in the AK-210 fermenter on medium containing n-hexadecane. Maximum indicators of SAS synthesis (concentration of extra cellular SAS is g/l; factor of emulsification of the cultural liquid 50%; SAS yield from the substrate 50%) have been observed at 60-70% concentration of dissolved oxygen from the saturation level with aerial oxygen (pH ) fractional supply of the substrate by portions each being -% every 5-6 h to a final volume concentration of % and with the use of 10% inoculate grown until mid-exponential phase on the medium with vol % of n-hexadecane. Implementation of the process of SAS biosynthesis with the fermentation equipment provided the possibility to increase almost two-fold the amount of the synthesized SAS and reduce -fold the time of cultivation of the producer strain compared with the growth in flasks at shake-flask propagator.

Let's take a look at an example of biosynthesis to get a better understanding of this process. Proteins are a substance in the body made up of amino acid chains that join together by peptide bonds in a process called protein synthesis. There are 20 amino acids that make up the building blocks of proteins. Amino acids join together by peptide bonds to create chains of amino acids called polypeptide chains. The type of protein the body needs will dictate which amino acids are used in building these chains and how they are folded together to create a macromolecule.

Dimethylsulfoniopropionate (DMSP) is one of the Earth's most abundant organosulfur molecules, a signalling molecule 1 , a key nutrient for marine microorganisms 2,3 and the major precursor for gaseous dimethyl sulfide (DMS). DMS, another infochemical in signalling pathways 4 , is important in global sulfur cycling 2 and affects the Earth's albedo, and potentially climate, via sulfate aerosol and cloud condensation nuclei production 5,6 . It was thought that only eukaryotes produce significant amounts of DMSP 7-9 , but here we demonstrate that many marine heterotrophic bacteria also produce DMSP, probably using the same methionine (Met) transamination pathway as macroalgae and phytoplankton 10 . We identify the first DMSP synthesis gene in any organism, dsyB, which encodes the key methyltransferase enzyme of this pathway and is a reliable reporter for bacterial DMSP synthesis in marine Alphaproteobacteria. DMSP production and dsyB transcription are upregulated by increased salinity, nitrogen limitation and lower temperatures in our model DMSP-producing bacterium Labrenzia aggregata LZB033. With significant numbers of dsyB homologues in marine metagenomes, we propose that bacteria probably make a significant contribution to oceanic DMSP production. Furthermore, because DMSP production is not solely associated with obligate phototrophs, the process need not be confined to the photic zones of marine environments and, as such, may have been underestimated.

Proses biosintesis steroid

proses biosintesis steroid

Dimethylsulfoniopropionate (DMSP) is one of the Earth's most abundant organosulfur molecules, a signalling molecule 1 , a key nutrient for marine microorganisms 2,3 and the major precursor for gaseous dimethyl sulfide (DMS). DMS, another infochemical in signalling pathways 4 , is important in global sulfur cycling 2 and affects the Earth's albedo, and potentially climate, via sulfate aerosol and cloud condensation nuclei production 5,6 . It was thought that only eukaryotes produce significant amounts of DMSP 7-9 , but here we demonstrate that many marine heterotrophic bacteria also produce DMSP, probably using the same methionine (Met) transamination pathway as macroalgae and phytoplankton 10 . We identify the first DMSP synthesis gene in any organism, dsyB, which encodes the key methyltransferase enzyme of this pathway and is a reliable reporter for bacterial DMSP synthesis in marine Alphaproteobacteria. DMSP production and dsyB transcription are upregulated by increased salinity, nitrogen limitation and lower temperatures in our model DMSP-producing bacterium Labrenzia aggregata LZB033. With significant numbers of dsyB homologues in marine metagenomes, we propose that bacteria probably make a significant contribution to oceanic DMSP production. Furthermore, because DMSP production is not solely associated with obligate phototrophs, the process need not be confined to the photic zones of marine environments and, as such, may have been underestimated.

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