Lub ntsiab mob rau lub neej ntawm txhua yam kab mob yog lub zog txuas ntxiv, uas yog siv rau ntau yam txheej txheem ntawm tes. Nyob rau tib lub sijhawm, qee qhov ntawm cov khoom siv sib xyaw tsis tuaj yeem siv tam sim ntawd, tab sis tuaj yeem hloov mus rau hauv cov khoom khaws cia. Lub luag hauj lwm ntawm lub reservoir yog ua los ntawm cov rog (lipids), uas muaj glycerol thiab fatty acids. Cov tom kawg yog siv los ntawm cov xov tooj ntawm tes ua roj. Hauv qhov no, fatty acids raug oxidized rau CO2 thiab H2O.
Fatty acid hauv paus
Fatty acids yog carbon chains ntawm ntau yam ntev (los ntawm 4 mus rau 36 atoms), uas yog tshuaj cais raws li carboxylic acids. Cov chains no tuaj yeem yog branched los yog unbranched thiab muaj ntau tus lej ntawm ob daim ntawv cog lus. Yog tias tom kawg tsis tuaj yeem ua tiav, fatty acids hu ua saturated (ib txwm rau ntau lipids ntawm tsiaj keeb kwm), thiab lwm yam -tsis saturated. Raws li kev npaj ntawm ob daim ntawv cog lus, fatty acids muab faib ua monounsaturated thiab polyunsaturated.
Feem ntau cov saw hlau muaj ntau tus lej ntawm cov pa roj carbon atoms, uas yog vim qhov txawv ntawm lawv cov khoom sib xyaw. Txawm li cas los xij, muaj kev sib txuas nrog tus lej khib ntawm qhov txuas. Cov oxidation ntawm ob hom kev sib txuas no txawv me ntsis.
yam ntxwv dav dav
Cov txheej txheem ntawm fatty acid oxidation yog complex thiab ntau theem. Nws pib nrog lawv nkag mus rau hauv lub xovtooj ntawm tes thiab xaus rau hauv txoj kev ua pa. Nyob rau tib lub sijhawm, cov theem kawg tau rov ua dua cov catabolism ntawm carbohydrates (lub voj voog Krebs, kev hloov pauv ntawm lub zog ntawm transmembrane gradient rau hauv daim ntawv cog lus macroergic). Cov khoom kawg ntawm cov txheej txheem yog ATP, CO2 thiab dej.
Oxidation ntawm fatty acids nyob rau hauv ib tug eukaryotic cell yog nqa tawm nyob rau hauv mitochondria (qhov feem ntau yam ntxwv qhov chaw ntawm lub zos), peroxisomes los yog endoplasmic reticulum.
Ntau yam (hom) ntawm oxidation
Muaj peb hom fatty acid oxidation: α, β thiab ω. Feem ntau, cov txheej txheem no tau ua los ntawm β-mechanism thiab yog nyob hauv mitochondria. Txoj kev omega yog ib qho kev hloov me me rau β-mechanism thiab tau ua nyob rau hauv endoplasmic reticulum, thaum lub alpha mechanism yog tus yam ntxwv ntawm tsuas yog ib hom fatty acid (phytanic).
Biochemistry ntawm fatty acid oxidation hauv mitochondria
Rau qhov yooj yim, cov txheej txheem ntawm mitochondrial catabolism yog conventionally muab faib ua 3 theem:
- ua kom thiab thauj mus rau mitochondria;
- oxidation;
- oxidation ntawm tsim acetyl-coenzyme A los ntawm Krebs lub voj voog thiab cov saw hluav taws xob thauj.
Kev ua kom muaj zog yog txheej txheem npaj uas hloov cov roj fatty acids rau hauv daim ntawv muaj rau kev hloov pauv biochemical, vim cov molecules lawv tus kheej tsis muaj zog. Tsis tas li ntawd, tsis muaj kev ua kom muaj zog, lawv tsis tuaj yeem nkag mus rau mitochondrial membranes. Cov theem no tshwm sim nyob rau ntawm daim nyias nyias ntawm mitochondria.
Qhov tseeb, oxidation yog ib kauj ruam tseem ceeb hauv cov txheej txheem. Nws suav nrog plaub theem, tom qab ntawd cov fatty acid hloov mus rau hauv Acetyl-CoA molecules. Cov khoom qub yog tsim thaum siv cov carbohydrates, kom cov kauj ruam tom ntej zoo ib yam li cov kauj ruam kawg ntawm aerobic glycolysis. Kev tsim ntawm ATP tshwm sim hauv cov saw hlau thauj khoom siv hluav taws xob, qhov twg lub zog ntawm cov khoom siv hluav taws xob tau siv los ua ib daim ntawv cog lus macroergic.
Nyob rau hauv cov txheej txheem ntawm fatty acid oxidation, ntxiv rau Acetyl-CoA, NADH thiab FADH molecules kuj tsim 2, uas kuj nkag mus rau hauv cov hlab pa raws li electron pub. Yog li ntawd, tag nrho lub zog tso zis ntawm lipid catabolism yog siab heev. Yog li, piv txwv li, oxidation ntawm palmitic acid los ntawm β-mechanism muab 106 ATP molecules.
Ua kom thiab hloov mus rau mitochondrial matrix
Fatty acids lawv tus kheej yog inert thiab tsis tuaj yeem oxidized. Kev ua kom coj lawv mus rau hauv daim ntawv muaj rau kev hloov pauv biochemical. Tsis tas li ntawd, cov molecules no tsis tuaj yeem nkag mus rau mitochondria tsis hloov pauv.
Lub ntsiab lus ntawm kev ua kom yogKev hloov pauv ntawm fatty acid rau hauv nws cov Acyl-CoA-thioester, uas tom qab ntawd ua rau oxidation. Cov txheej txheem no yog ua los ntawm cov enzymes tshwj xeeb - thiokinases (Acyl-CoA synthetases) txuas rau sab nrauv ntawm mitochondria. Cov tshuaj tiv thaiv tshwm sim hauv 2 theem, cuam tshuam nrog kev siv zog ntawm ob ATP.
Peb yam yuav tsum tau ua kom ua:
- ATF;
- HS-CoA;
- Mg2+.
Ua ntej, fatty acid reacts nrog ATP los tsim acyladenylate (ib nrab). Uas, nyob rau hauv lem, reacts nrog HS-CoA, thiol pab pawg neeg ntawm displaces AMP, tsim ib tug thioether daim ntawv cog lus nrog cov carboxyl pawg. Yog li ntawd, cov tshuaj acyl-CoA yog tsim - fatty acid derivative, uas yog thauj mus rau mitochondria.
Kev thauj mus los rau mitochondria
Cov kauj ruam no hu ua transesterification nrog carnitine. Kev hloov pauv ntawm acyl-CoA mus rau mitochondrial matrix yog ua los ntawm cov pores nrog kev koom tes ntawm carnitine thiab tshwj xeeb enzymes - carnitine acyltransferases.
Rau kev thauj mus los hla cov membranes, CoA yog hloov los ntawm carnitine los ua acyl-carnitine. Cov khoom no raug thauj mus rau hauv matrix los ntawm acyl-carnitine / carnitine transporter uas yooj yim rau diffusion.
Inside lub mitochondria, ib qho kev cuam tshuam rov qab tshwm sim, muaj nyob rau hauv lub detachment ntawm retinal, uas rov nkag mus rau hauv daim nyias nyias, thiab kev kho dua ntawm acyl-CoA (qhov no, "hauv zos" coenzyme A yog siv, thiab tsis yog tus uas daim ntawv cog lus tau tsimnyob rau theem ua kom).
Cov tshuaj tiv thaiv tseem ceeb ntawm fatty acid oxidation los ntawm β-mechanism
Hom kev siv lub zog yooj yim tshaj plaws ntawm cov roj fatty acids yog β-oxidation ntawm cov saw hlau uas tsis muaj ob daim ntawv cog lus, uas cov roj carbon ntau yog txawm tias. Lub substrate rau cov txheej txheem no, raws li tau sau tseg saum toj no, yog acyl coenzyme A.
Cov txheej txheem ntawm β-oxidation ntawm fatty acids muaj 4 yam tshuaj:
- Dehydrogenation yog kev sib cais ntawm hydrogen los ntawm β-carbon atom nrog tsim ntawm ob daim ntawv cog lus ntawm cov saw txuas nyob rau hauv α thiab β-txoj hauj lwm (thawj thiab thib ob atoms). Yog li ntawd, enoyl-CoA yog tsim. Cov tshuaj tiv thaiv enzyme yog acyl-CoA dehydrogenase, uas ua ke nrog coenzyme FAD (tom kawg raug txo rau FADH2).
- Hydration yog qhov sib ntxiv ntawm cov dej molecule rau enoyl-CoA, ua rau tsim L-β-hydroxyacyl-CoA. Ua los ntawm eonyl-CoA-hydratase.
- Dehydrogenation - oxidation ntawm cov khoom ntawm cov tshuaj tiv thaiv yav dhau los los ntawm NAD-dependent dehydrogenase nrog kev tsim ntawm β-ketoacyl-coenzyme A. Nyob rau hauv rooj plaub no, NAD yog txo rau NADH.
- Cleavage ntawm β-ketoacyl-CoA rau acetyl-CoA thiab 2-carbon shortened acyl-CoA. Cov tshuaj tiv thaiv yog ua raws li kev ua ntawm thiolase. Yam yuavtsum tau kawm uantej yog muaj HS-CoA dawb.
Tom qab ntawd txhua yam pib dua nrog thawj cov tshuaj tiv thaiv.
Kev rov ua dua ntawm txhua theem yog ua kom txog thaum tag nrho cov saw hlau ntawm fatty acid hloov mus rau hauv molecules ntawm acetyl-coenzyme A.
Kev tsim ntawm Acetyl-CoA thiab ATP ntawm qhov piv txwv ntawm palmitoyl-CoA oxidation
Thaum kawg ntawm txhua lub voj voog, acyl-CoA, NADH thiab FADH2 molecules raug tsim nyob rau hauv ib qho nyiaj, thiab cov saw hlau acyl-CoA-thioether ua luv luv los ntawm ob lub atoms. Los ntawm kev xa cov hluav taws xob mus rau cov saw hlau electrotransport, FADH2 muab ib thiab ib nrab ATP molecules, thiab NADH ob. Yog li ntawd, 4 ATP molecules tau txais los ntawm ib lub voj voog, tsis suav lub zog tawm los ntawm acetyl-CoA.
Cov saw hlau palmitic muaj 16 carbon atoms. Qhov no txhais tau hais tias nyob rau theem ntawm oxidation 7 lub voj voog yuav tsum tau ua nrog kev tsim ntawm yim acetyl-CoA, thiab lub zog tawm los ntawm NADH thiab FADH 2 hauv qhov no yuav yog 28 ATP molecules. (4 × 7). Lub oxidation ntawm acetyl-CoA kuj mus rau kev tsim lub zog, uas yog khaws cia raws li cov khoom ntawm Krebs lub voj voog nkag mus rau hauv cov saw hluav taws xob thauj.
Tag nrho cov txiaj ntsig ntawm cov kauj ruam oxidation thiab Krebs voj voog
Raws li qhov tshwm sim ntawm oxidation ntawm acetyl-CoA, 10 ATP molecules tau txais. Txij li thaum catabolism ntawm palmitoyl-CoA yields 8 acetyl-CoA, lub zog tawm los yuav yog 80 ATP (10 × 8). Yog tias koj ntxiv qhov no rau qhov tshwm sim ntawm oxidation ntawm NADH thiab FADH2, koj tau txais 108 molecules (80 + 28). Los ntawm cov nyiaj no, 2 ATP yuav tsum tau muab rho tawm, uas tau mus qhib cov roj fatty acid.
Qhov kawg sib npaug rau oxidation ntawm palmitic acid yuav yog: palmitoyl-CoA + 16 O2 + 108 Pi + 80 ADP=CoA + 108 ATP + 16 CO2 + 16 H2O.
Xaiv lub zog tso tawm
Lub zog tso pa tawmntawm catabolism ntawm ib qho fatty acid nyob ntawm seb muaj pes tsawg tus carbon units hauv nws cov saw hlau. Tus naj npawb ntawm ATP molecules yog xam los ntawm cov mis:
[4(n/2 - 1) + n/2×10] - 2, qhov twg 4 yog tus nqi ntawm ATP tsim los ntawm txhua lub voj voog vim NADH thiab FADH2, (n/2 - 1) yog tus lej ntawm lub voj voog, n / 2 × 10 yog lub zog tawm los ntawm oxidation ntawm acetyl- CoA, thiab 2 yog tus nqi ntawm kev ua haujlwm.
Txoj kev xav
Oxidation ntawm unsaturated fatty acids muaj qee yam peculiarities. Yog li, qhov nyuaj ntawm oxidizing chains nrog ob daim ntawv cog lus nyob rau hauv qhov tseeb tias tom kawg tsis tuaj yeem raug rau enoyl-CoA-hydratase vim qhov tseeb tias lawv nyob hauv txoj haujlwm cis. Qhov teeb meem no raug tshem tawm los ntawm enoyl-CoA isomerase, vim tias daim ntawv cog lus tau txais kev hloov pauv. Yog li ntawd, cov molecule yuav zoo ib yam nkaus rau cov khoom ntawm thawj theem ntawm beta-oxidation thiab muaj peev xwm undergo hydration. Cov chaw uas muaj tib daim ntawv cog lus oxidize tib yam li cov kua qaub saturated.
Qee lub sij hawm enoyl-CoA-isomerase tsis txaus los txuas ntxiv cov txheej txheem. Qhov no siv rau cov chains uas lub cis9-cis12 configuration yog tam sim no (ob daim ntawv cog lus ntawm 9th thiab 12th carbon atoms). Ntawm no, tsis tsuas yog lub configuration yog ib tug hindrance, tab sis kuj txoj hauj lwm ntawm ob daim ntawv cog lus nyob rau hauv lub saw. Cov tom kawg raug kho los ntawm enzyme 2,4-dienoyl-CoA reductase.
Catabolism ntawm khib fatty acids
Hom kua qaub no yog qhov zoo rau feem ntau cov lipids ntawm ntuj (natural) keeb kwm. Qhov no tsim ib qho nyuaj, txij li txhua lub voj voogimplies shortening los ntawm ib tug txawm tus lej ntawm cov txuas. Vim li no, lub cyclic oxidation ntawm cov roj fatty acids ntau dua ntawm cov pab pawg no txuas ntxiv mus txog rau thaum lub ntsej muag ntawm 5-carbon compound raws li cov khoom, uas yog cleaved rau hauv acetyl-CoA thiab propionyl-coenzyme A. Ob lub tebchaw nkag mus rau lwm lub voj voog ntawm peb cov tshuaj tiv thaiv., raws li qhov tshwm sim ntawm succinyl-CoA yog tsim. Nws yog tus uas nkag mus rau lub voj voog Krebs.
Ntawm oxidation hauv peroxisomes
Nyob rau hauv peroxisomes, fatty acid oxidation tshwm sim los ntawm beta mechanism uas zoo sib xws, tab sis tsis zoo ib yam, rau mitochondrial. Nws kuj tseem muaj 4 theem, ua tiav hauv kev tsim cov khoom hauv daim ntawv ntawm acetyl-CoA, tab sis nws muaj ntau qhov sib txawv tseem ceeb. Yog li, hydrogen cais tawm ntawm lub dehydrogenation theem tsis rov qab FAD, tab sis dhau mus rau oxygen nrog tsim hydrogen peroxide. Tom qab tam sim ntawd undergoes cleavage nyob rau hauv qhov kev txiav txim ntawm catalase. Raws li qhov tshwm sim, lub zog uas tuaj yeem siv los ua ke ATP hauv cov kab mob ua pa yog dissipated li cua sov.
Qhov sib txawv tseem ceeb thib ob yog tias qee qhov peroxisome enzymes tshwj xeeb rau qee yam tsawg dua fatty acids thiab tsis muaj nyob hauv mitochondrial matrix.
Qhov tshwj xeeb ntawm peroxisomes ntawm daim siab hlwb yog tias tsis muaj cov khoom siv enzymatic ntawm lub voj voog Krebs. Yog li ntawd, raws li qhov tshwm sim ntawm beta-oxidation, cov khoom siv luv luv tau tsim, uas tau thauj mus rau mitochondria rau oxidation.
