Cholesterol is a 27-carbon molecule shown in the figure below. Each line in this figure represents a bond between two carbon atoms.
膽固醇是含有27個碳原子的分子。每一條線表示兩個碳原子之間的鍵。
1769年
François Poulletier de la Salle first identified cholesterol in solid form in gallstones in 1769. However, it was not until 1815 that chemist Michel Eugène Chevreul named the compound "cholesterine".
François Poulletier de la Salle (September 30, 1719 in Lyon – March 20, 1788 in Paris) was a French doctor and chemist. In about 1758, he isolated for the first time the crystals from cholesterol.
Cholesterol, a steroid alcohol, can be “free” or “unesterified” (“UC” as we say, which stands for unesterified cholesterol) which is its active form, or it can exist in its “esterified” or storage form which we call a cholesterol ester (“CE”). The diagram above shows a free (i.e., UC) molecule of cholesterol. An esterified variant (i.e., CE) would have an “attachment” where the arrow is pointing to the hydroxyl group on carbon #3, aptly named the “esterification site.”
膽固醇,一種類固醇的醇(酒精) ,可以是“游離”或“酯化”(unesterified cholesterol, UC,代表未酯化的膽固醇),這是它活性的形式;或者它可以在它的“酯化”或存儲的形式存在,我們稱之為膽固醇酯(cholesterol ester, CE)。
上面的圖表顯示一個游離的膽固醇分子(即,UC)。酯化的變體(即CE)有一個“附屬物”,箭頭指向的羥基的碳#3,命名為“酯化的地點。”
Cholesterol, a steroid alcohol, can be “free” or “unesterified” (“UC” as we say, which stands for unesterified cholesterol) which is its active form, or it can exist in its “esterified” or storage form which we call a cholesterol ester (“CE”). The diagram above shows a free (i.e., UC) molecule of cholesterol. An esterified variant (i.e., CE) would have an “attachment” where the arrow is pointing to the hydroxyl group on carbon #3, aptly named the “esterification site.”
膽固醇,一種類固醇的醇(酒精) ,可以是“游離”或“酯化”(unesterified cholesterol, UC,代表未酯化的膽固醇),這是它活性的形式;或者它可以在它的“酯化”或存儲的形式存在,我們稱之為膽固醇酯(cholesterol ester, CE)。
上面的圖表顯示一個游離的膽固醇分子(即,UC)。酯化的變體(即CE)有一個“附屬物”,箭頭指向的羥基的碳#3,命名為“酯化的地點。”
Cholesterol, a steroid alcohol, can be “free” or “unesterified” (“UC” as we say, which stands for unesterified cholesterol) which is its active form, or it can exist in its “esterified” or storage form which we call a cholesterol ester (“CE”). The diagram above shows a free (i.e., UC) molecule of cholesterol. An esterified variant (i.e., CE) would have an “attachment” where the arrow is pointing to the hydroxyl group on carbon #3, aptly named the “esterification site.”
膽固醇,一種類固醇的醇(酒精) ,可以是“游離”或“酯化”(unesterified cholesterol, UC,代表未酯化的膽固醇),這是它活性的形式;或者它可以在它的“酯化”或存儲的形式存在,我們稱之為膽固醇酯(cholesterol ester, CE)。
上面的圖表顯示一個游離的膽固醇分子(即,UC)。酯化的變體(即CE)有一個“附屬物”,箭頭指向的羥基的碳#3,命名為“酯化的地點。”
All animal cells manufacture cholesterol for their use, with relative production rates varying by cell type and organ function.
所有的動物細胞都會生產膽固醇為它們的使用,只是依據不同的細胞類型和器官的功能而有不同的生產率。
About 20–25% of total daily cholesterol production occurs in the liver; other sites of higher synthesis rates include the intestines, adrenal glands, and reproductive organs.
約20-25%的每日總膽固醇生產發生在肝臟;其他合成速率較高的包括腸,腎上腺和生殖器官。
乙醯-CoA
乙醯輔酶A(Acetyl coenzyme A or acetyl-CoA )
acetyl [æsitil] n.[化]乙醯基,醋酸基
醯基(「醯」,拼音:xiān,注音:ㄒㄧ;英語:acyl group)是指從含氧酸,包括無機酸中除去一個或多個羥基基團的衍生的官能團。
羥ㄑ|ㄤˇ :着一種由氫、氧原子組成的原子團。
β-氧化指的是脂肪酸氧化分解,最終產生乙醯輔酶A(Acetyl-CoA)和酮體的過程。
Synthesis within the body starts with the mevalonate pathway where two molecules of acetyl CoA condense to form acetoacetyl-CoA.
在體內合成開始於甲羥戊酸途徑,其中的乙酰輔酶A縮合成兩分子以形成乙酰乙酰CoA。
Synthesis within the body starts with the mevalonate pathway where two molecules of acetyl CoA condense to form acetoacetyl-CoA.
This is followed by a second condensation between acetyl CoA and acetoacetyl-CoA to form 3-hydroxy-3-methylglutaryl CoA (HMG-CoA).[37]
這之後是乙酰CoA和乙酰乙酰CoA之間的第二縮合以形成3-羥基-3-甲基輔酶A(HMG-COA)。[37]
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羥甲基戊二酸單醯輔酶A(3-hydroxy-3-methylglutaryl-CoA,簡稱「HMG-CoA」)也稱為「β-羥基-β-甲戊二酸單醯輔酶A」或「3-羥基-3-甲戊二酸單醯輔酶A」,是一種重要的脂類代謝中間產物。
合成β-羥-β-甲戊二酸單醯輔酶A需要三分子的乙醯輔酶A,其中兩分子的乙醯輔酶A先在硫解酶的作用下縮合成為乙醯乙醯輔酶A,後者在β-羥-β-甲戊二酸單醯輔酶A合酶的作用下與另一分子的乙醯輔酶A合成出β-羥-β-甲戊二酸單醯輔酶A。
該物質可以走向兩種途徑:在β-羥-β-甲戊二酸單醯輔酶A裂解酶的作用下裂解為乙醯乙酸,繼而生成丙酮和β-D-羥丁酸,這三者被稱為酮體;在β-羥-β-甲戊二酸單醯輔酶A還原酶的作用下還原為甲羥戊酸,繼而參與動植物中萜類、固醇類化合物的合成。
故植物中不少次生代謝產物或激素是由這種化合物衍生而來的,如赤黴素、脫落酸等,動物體內則以此合成膽固醇及各種類固醇激素等。
This molecule is then reduced to mevalonate by the enzyme HMG-CoA reductase.
該分子隨後通過酶HMG-CoA還原酶降低到甲羥戊酸。
Production of mevalonate is the rate-limiting and irreversible step in cholesterol synthesis and is the site of action for statins (a class of cholesterol lowering drugs).
生產甲羥戊酸是在膽固醇合成中限速和不可逆轉的步驟,是作用部位為他汀類藥物(類的降膽固醇的藥物)。
Evaluate is finally converted to isopentenyl pyrophosphate (IPP) through two phosphorylation steps and one decarboxylation step that requires ATP.
甲羥戊酸通過兩個步驟的磷酸化和一個步驟的脫羧最終轉化成異戊烯焦(IPP)。焦磷酸異戊烷
Three molecules of isopentenyl pyrophosphate condense to form farnesyl pyrophosphate through the action of geranyl transferase.
三個分子的異戊烯焦冷凝以形成通過香葉基轉移酶的作用下法尼焦磷酸。
在膽固醇合成中,需要從牻牛兒基(geranyl)和異戊烯焦磷酸生成法呢基(farnesyl)焦磷酸。
Two molecules of farnesyl pyrophosphate then condense to form squalene by the action of squalene synthase in the endoplasmic reticulum.[37]
兩個分子的法尼基焦磷酸然後在內質網經由角鯊烯合酶squalene synthase的作用縮合形成角鯊烯Squalene
內質網(英語:Endoplasmic reticulum, ER)是在真核生物細胞中由膜圍成的隧道系統,為細胞中的重要胞器。
鯊烯(Squalene),又稱角鯊烯,是一種開鏈三萜類化合物。因最初從鯊魚肝油中提取得到,故得名鯊烯。隨後發現鯊魚卵油及其他魚中也含有它,現在發現它的分布比預想的要廣泛許多,真菌及人耳垢中含有少量。鯊烯是膽固醇生物合成中間體之一,是所有類固醇類物質的生物合成前體。
Oxidosqualene cyclase then cyclizes squalene to form lanosterol.環氧角鯊烯環化酶然後環化角鯊烯以形成羊毛甾醇。
羊毛甾醇;羊毛脂醇;異膽甾醇;羊毛脂甾醇
Finally, lanosterol is converted to cholesterol through a 19-step process.
最後,羊毛甾醇是通過一個19步驟的過程轉化為膽固醇。
內源性物質,是體內代謝中產生的活性物質及最終產物,比如NH3、胺類、激素、膽色素、神經遞質等都可以稱為內源性物質。
Endogenous substances and processes are those that originate from within an organism, tissue, or cell.
The word endogenous /ɛnˈdɒdʒɪnəs/ derives from the Ancient Greek ἐνδο-, "inside" and -γενής, "coming from".
Exogenous
exogenous /,ɛks'odʒənəs/ (a.)外生的來源
About 25% of our daily “intake” of cholesterol – roughly 300 to 500 mg — comes from what we eat (called exogenous cholesterol), and the remaining 75% of our “intake” of cholesterol — roughly 800 to 1,200 mg – is made by our body (called endogenous production).
約25%的我們每天膽固醇的“攝入”的 - 大約300至500毫克 - 來自我們吃什麼(稱為外源性膽固醇),和我們的膽固醇“攝入”的其餘75% - 大約800至1200毫克 - 由我們的身體(稱為內源性產生)。
To put these amounts in context, consider that total body stores of cholesterol are about 30 to 40 gm (i.e., 30,000 to 40,000 mg) and most of this resides within our cell membranes.
全身存儲膽固醇約30〜40克(即30,000到40,000毫克),大多數存在於我們的細胞膜內。
Every cell in the body can produce cholesterol and thus very few cells actually require a delivery of cholesterol.
在身體每個細胞都可產生膽固醇,因而很少有細胞實際上需要膽固醇的輸送。
To put these amounts in context, consider that total body stores of cholesterol are about 30 to 40 gm (i.e., 30,000 to 40,000 mg) and most of this resides within our cell membranes.
全身存儲膽固醇約30〜40克(即30,000到40,000毫克),大多數存在於我們的細胞膜內。
Every cell in the body can produce cholesterol and thus very few cells actually require a delivery of cholesterol.
在身體每個細胞都可產生膽固醇,因而很少有細胞實際上需要膽固醇的輸送。
Only free or unesterified cholesterol (UC) can be absorbed through gut enterocytes. In other words, cholesterol esters (CE) cannot be absorbed because of the bulky side chains they carry.
只有游離或未酯化的膽固醇(UC)可通過腸道腸吸收。換言之,膽固醇酯(CE)不能被吸收,因為它們攜帶笨重的側鏈。
小腸的絨毛細胞
腸上皮細胞(enterocyte)
腸黏膜細胞(enterocyte)
Only free or unesterified cholesterol (UC) can be absorbed through gut enterocytes. In other words, cholesterol esters (CE) cannot be absorbed because of the bulky side chains they carry.
只有游離或未酯化的膽固醇(UC)可通過腸道腸吸收。換言之,膽固醇酯(CE)不能被吸收,因為它們攜帶笨重的側鏈。
小腸的絨毛細胞
腸上皮細胞(enterocyte)
腸黏膜細胞(enterocyte)
Much (> 50%) of the cholesterol we ingest from food is esterified (CE), hence we don’t actually absorb much, if any, exogenous cholesterol (i.e., cholesterol in food).
大部分(> 50%)我們從食物攝取的是膽固醇酯(CE),因此,我們實際上吸收並不多外源性膽固醇(即,食品中的膽固醇)。
CE can be de-esterified by pancreatic lipases and esterolases – enzymes that break off the side branches and render CE back to UC — so some ingested CE can be converted to UC.
膽固醇酯可以被胰脂肪酶(pancreatic lipases)和酯解酶(esterolases) - 折斷側枝並將CE轉回UC的酶-進行脫酯,所以一些攝入的CE可以被轉換為UC。
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成人主要是利用胰臟分泌的脂解脢,配合膽汁提供膽鹽幫助,將脂肪分解以供吸收。
酯解酶(esterase)
Furthermore, most of the unesterified cholesterol (UC) in our gut (on the order of about 85%) is actually of endogenous origin (meaning it was synthesized in bodily cells and returned to the liver), which ends up in the gut via biliary secretion and ultimately gets re-absorbed by the gut enterocyte.
•此外,在我們的腸道中大部分(約85%)的未酯化膽固醇(UC)實際上是內源性來源的(意思是它是在身體細胞中合成並返回到肝臟),其通過膽汁的分泌而到達腸道,最終由得到由小腸黏膜細胞重新吸收。
The liver is only able to efflux (send out via bile into the gut) UC, but not CE, from hepatocytes (liver cells) to the biliary system.
Liver CE cannot be excreted into bile. So, if the liver is going to excrete CE into bile and ultimately the gut, it needs to de-esterify it using enzymes called cholesterol esterolases which can convert liver CE to UC.
肝臟是只能外排(經由排出膽汁進入腸道)UC,而不是CE,從肝細胞到膽道系統。肝臟的CE無法排泄到膽汁。因此,如果肝臟是要排泄CE到膽汁和最終到腸道,它需要使用一種酶稱為膽固醇酯解酶來脫脂化,酯解酶把肝臟的CE轉化為UC。
Also realize that the number one way for the liver to rid itself of cholesterol is to convert the cholesterol into a bile acid, efflux that to the bile (via a transporter called ABCB11) and excrete the bile acids in the stool (typically most bile acids are reabsorbed at the ileum).
•還認識到,肝臟要擺脫自身的膽固醇最好的方式是將膽固醇轉化成膽汁酸,外排到膽汁(通過稱為ABCB11轉運)並將膽汁酸經糞便中排泄(通常為大多數膽汁酸會在迴腸再吸收)。
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Also realize that the number one way for the liver to rid itself of cholesterol is to convert the cholesterol into a bile acid, efflux that to the bile (via a transporter called ABCB11) and excrete the bile acids in the stool (typically most bile acids are reabsorbed at the ileum).
•還認識到,肝臟要擺脫自身的膽固醇最好的方式是將膽固醇轉化成膽汁酸,外排到膽汁(通過稱為ABCB11轉運)並將膽汁酸經糞便中排泄(通常為大多數膽汁酸會在迴腸再吸收)。
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膽汁酸鹽輸出泵蛋白(ABCB11)
ABCB11基因編碼的膽鹽輸出泵(BSEP)是肝內膽汁酸輸出的主要載體,是膽汁流形成的重要驅動力。
肝細胞轉運蛋白(ABCB)11[即膽鹽輸出泵(BSEP)]
人類ABCB11基因編碼產生膽鹽輸出泵(BSEP),BSEP是位於肝細胞毛細膽管面上的重要轉運體,將膽鹽從肝細胞內轉運到毛細膽管中,是形成膽汁流的最主要動力。
ATP-binding cassette, sub-family B member 11 also known as ABCB11 is a protein which in humans is encoded by the ABCB11 gene.
Also realize that the number one way for the liver to rid itself of cholesterol is to convert the cholesterol into a bile acid, efflux that to the bile (via a transporter called ABCB11) and excrete the bile acids in the stool (typically most bile acids are reabsorbed at the ileum).
•還認識到,肝臟要擺脫自身的膽固醇最好的方式是將膽固醇轉化成膽汁酸,外排到膽汁(通過稱為ABCB11轉運)並將膽汁酸經糞便中排泄(通常為大多數膽汁酸會在迴腸再吸收)。
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