Topic
Sterol
About: Sterol is a(n) research topic. Over the lifetime, 8117 publication(s) have been published within this topic receiving 309926 citation(s). The topic is also known as: sterols & sterol lipids.
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TL;DR: It is indicated that inferences drawn from sterol distributions regarding sources of organic matter must be made with caution and should be supported using other lipid data, and that in ancient sediments and crude oils a high proportion of C 29 steranes need not indicate that most of the organic matter was derived from vascular plants.
Abstract: A review of literature on the occurrence of 4-desmethyl sterols in unicellular algae indicates that few sterols are sufficiently restricted in distribution to be considered unambiguous markers for specific algal groups. Almost all of the 4-desmethyl sterols found in higher plants occur in marine algae, sometimes as major constituents, so sterol distributions do not always allow to distinguish between marine or terrigenous organic matter. Some of the problems associated with the use of sterols as markers for specific sources are highlighted by comparison of the sterol distribution in selected marine sediments and seawater samples. Although each sediment represents a very different depositional environment the sterol distributions are surprisingly similar. The sterol distributions in a saline Antarctic lake and samples of particulate matter from oligotrophic waters off the east Australian coast show that marine phytoplankton biosynthesize a wide range of sterols, including large amounts of 24-ethylcholest-5-en-3β-ol which is often used as a marker for terrigenous organic matter. Similar distributions occur in marine sediments from the upwelling area off Peru and in temperate intertidal sediments despite large differences in algal productivity between the two areas. In deeper sediments, most of the sterols are not derived from phytoplankton but from higher plants. These data indicate that inferences drawn from sterol distributions regarding sources of organic matter must be made with caution and should be supported using other lipid data. It further follows that in ancient sediments and crude oils a high proportion of C 29 steranes need not indicate that most of the organic matter was derived from vascular plants.
1,554 citations
TL;DR: Data suggest that ABCG5 and ABCG8 normally cooperate to limit intestinal absorption and to promote biliary excretion of sterols, and that mutated forms of these transporters predispose to sterol accumulation and atherosclerosis.
Abstract: In healthy individuals, acute changes in cholesterol intake produce modest changes in plasma cholesterol levels. A striking exception occurs in sitosterolemia, an autosomal recessive disorder characterized by increased intestinal absorption and decreased biliary excretion of dietary sterols, hypercholesterolemia, and premature coronary atherosclerosis. We identified seven different mutations in two adjacent, oppositely oriented genes that encode new members of the adenosine triphosphate (ATP)-binding cassette (ABC) transporter family (six mutations in ABCG8 and one in ABCG5) in nine patients with sitosterolemia. The two genes are expressed at highest levels in liver and intestine and, in mice, cholesterol feeding up-regulates expressions of both genes. These data suggest that ABCG5 and ABCG8 normally cooperate to limit intestinal absorption and to promote biliary excretion of sterols, and that mutated forms of these transporters predispose to sterol accumulation and atherosclerosis.
1,519 citations
TL;DR: Recent advances that explain how cells employ an ensemble of membrane-embedded proteins to monitor sterol concentrations and adjust sterol synthesis and uptake are discussed.
Abstract: Cholesterol is an essential component of animal cell membranes, and its concentration is tightly controlled by a feedback system that operates at transcriptional and posttranscriptional levels. Here, we discuss recent advances that explain how cells employ an ensemble of membrane-embedded proteins to monitor sterol concentrations and adjust sterol synthesis and uptake.
1,379 citations
TL;DR: These regulated proteolytic cleavage reactions are ultimately responsible for controlling the level of cholesterol in membranes, cells, and blood.
Abstract: The integrity of cell membranes is maintained by a balance between the amount of cholesterol and the amounts of unsaturated and saturated fatty acids in phospholipids. This balance is maintained by membrane-bound transcription factors called sterol regulatory element-binding proteins (SREBPs) that activate genes encoding enzymes of cholesterol and fatty acid biosynthesis. To enhance transcription, the active NH2-terminal domains of SREBPs are released from endoplasmic reticulum membranes by two sequential cleavages. The first is catalyzed by Site-1 protease (S1P), a membrane-bound subtilisin-related serine protease that cleaves the hydrophilic loop of SREBP that projects into the endoplasmic reticulum lumen. The second cleavage, at Site-2, requires the action of S2P, a hydrophobic protein that appears to be a zinc metalloprotease. This cleavage is unusual because it occurs within a membrane-spanning domain of SREBP. Sterols block SREBP processing by inhibiting S1P. This response is mediated by SREBP cleavage-activating protein (SCAP), a regulatory protein that activates S1P and also serves as a sterol sensor, losing its activity when sterols overaccumulate in cells. These regulated proteolytic cleavage reactions are ultimately responsible for controlling the level of cholesterol in membranes, cells, and blood.
1,267 citations
TL;DR: The structure of the sterol 26-hydroxylase cDNA reveals it to be a mitochondrial cytochrome P-450, and blotting experiments revealed that the mRNA for this enzyme is expressed in many tissues and that it is encoded by a low copy number gene in the rabbit genome.
Abstract: The conversion of cholesterol into bile acids in the liver represents the major catabolic pathway for the removal of cholesterol from the body. In this complex biosynthetic pathway, at least 10 enzymes modify both the ring structure and side chain of cholesterol, resulting in the formation of the primary bile acids, cholic acid, and chenodeoxycholic acid. To gain insight into the details and regulation of this pathway, we have used protein sequencing and molecular cloning techniques to isolate and characterize a cDNA encoding the rabbit mitochondrial sterol 26-hydroxylase. This enzyme catalyzes the first step in the oxidation of the side chain of sterol intermediates in the biosynthesis of bile acids. The structure of the sterol 26-hydroxylase, as deduced by both DNA sequence analysis of the cDNA and protein sequence analysis, reveals it to be a mitochondrial cytochrome P-450. A signal sequence of 36 residues precedes a coding region of 499 amino acids, predicting a molecular weight of 56,657 for the mature protein. The identity of the 26-hydroxylase cDNA was further confirmed by expression in monkey COS cells employing a versatile eukaryotic expression vector. Blotting experiments revealed that the mRNA for this enzyme is expressed in many tissues and that it is encoded by a low copy number gene in the rabbit genome.
1,139 citations