argininosuccinate synthase

アルギニノコハク酸合成酵素、アルギニノコハク酸シンターゼ

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/01/29 14:06:47」(JST)

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Argininosuccinate synthetase
Crystallographic structure of human argininosuccinate synthetase.
Identifiers
EC number	6.3.4.5
CAS number	9023-58-9
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / EGO
Search PMC articles PubMed articles NCBI proteins

Argininosuccinate synthetase 1
Identifiers
Symbol	ASS1
Entrez	445
HUGO	758
OMIM	603470
RefSeq	NM_000050
UniProt	P00966
Other data
EC number	6.3.4.5
Locus	Chr. 9 q34.1

Reaction catalyzed by argininosuccinate synthetase. Adapted from Goto et al. 2003.

Argininosuccinate synthetase
crystal structure of thermus thermophilus hb8 argininosuccinate synthetase in complex with atp and citrulline
Identifiers
Symbol	Arginosuc_synth
Pfam	PF00764
Pfam clan	CL0039
InterPro	IPR001518
PROSITE	PDOC00488
SCOP	1kp2
SUPERFAMILY	1kp2
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Argininosuccinate synthase or synthetase (ASS) (EC 6.3.4.5) is an enzyme that catalyzes the synthesis of argininosuccinate from citrulline and aspartate.

ASS is responsible for the third step of the urea cycle and one of the reactions of the citrulline-NO cycle.

Genetic structure

The gene that encodes for this enzyme, ASS, is located on chromosome 9. In humans, ASS is expressed mostly in the cells of liver and kidney. The expressed ASS gene is at least 65 kb in length, including at least 12 introns.

Enzyme mechanism

In the first step of the catalyzed reaction, citrulline attacks the α-phosphate of ATP to form citrulline adenylate, a reactive intermediate. The attachment of AMP to the ureido (urea-like) group on citrulline activates the carbonyl center for subsequent nucleophilic attack. This activation facilitates the second step, in which the α-amino group of aspartate attacks the ureido group. Attack by aspartate is the rate-limiting step of the reaction. This step produces free AMP and L-argininosuccinate.

Thermodynamically, adenylation of the citrulline ureido group is more favorable than the analogous phosphorylation. Additionally, attack by citrulline at the α-phosphate of ATP produces an equivalent of pyrophosphate, which can be hydrolyzed in a thermodynamically favorable reaction to provide additional energy to drive the adenylation.

Enzyme structure

Quaternary structure

Argininosuccinate synthetase is a homotetramer, with each subunit consisting of 412 residues. The interfaces between subunits contain a number of salt bridges and hydrogen bonds, and the C-terminus of each subunit is involved in oligomerization by interacting with the C-termini and nucleotide-binding domains of the other subunits.

Active site

X-ray crystal structures have been generated for argininosuccinate synthetase from Thermus thermophilus, E. coli, Thermotoga maritime, and Homo sapiens. In ASS from T. thermophilus, E. coli, and H. sapiens, citrulline and aspartate are tightly bound in the active site by interactions with serine and arginine residues; interactions of the substrates with other residues in the active site vary by species. In T. thermophilus, the ureido group of citrulline appears to be repositioned during nucleophilic attack to attain sufficient proximity to the α-phosphate of ATP. In E. coli, it is suggested that binding of ATP causes a conformational shift that brings together the nucleotide-binding domain and the synthetase domain. An argininosuccinate synthetase structure with a bound ATP in the active site has not been attained, although modeling suggests that the distance between ATP and the ureido group of citrulline is smaller in human argininosuccinate synthetase than in the E. coli variety, so it is likely that a much smaller conformational change is necessary for catalysis. The ATP binding domain of argininosuccinate synthetase is similar to that of other N-type ATP pyrophosphatases.

Active site of argininosuccinate synthetase shown with bound citrulline, ATP, and aspartate interacting with select active site residues. Modeled using PyMol from PDB 1J1Z.

Biological function

Argininosuccinate synthetase is involved in the synthesis of creatine, polyamines, arginine, urea, and nitric oxide.

Arginine synthesis

The transformation of citrulline into argininosuccinate is the rate-limiting step in arginine synthesis. The activity of argininosuccinate synthetase in arginine synthesis occurs largely in at the outer mitochondrial membrane of periportal liver cells as part of the urea cycle, with some activity occurring in cortical kidney cells. Genetic defects that cause incorrect localization of argininosuccinate synthetase to the outer mitochondrial membrane cause type II citrullinemia.

In fetuses and infants, arginine is also produced via argininosuccinate synthetase activity in intestinal cells, presumably to supplement the low level of arginine found in mother’s milk. Expression of argininosuccinate synthetase in the intestines ceases after two to three years of life.

It is thought that regulation of argininosuccinate synthetase activity in arginine synthesis occurs primarily at the transcriptional level in response to glucocorticoids, cAMP, glucagon, and insulin. It has also been demonstrated in vitro that arginine down-regulates argininosuccinate synthetase expression, while citrulline up-regulates it.

Citrulline-NO cycle

The enzyme endothelial nitric oxide synthase produces nitric oxide from arginine in endothelial cells. Argininosuccinate synthetase and argininosuccinate lyase recycle citrulline, a byproduct of nitric oxide production, into arginine. Since nitric oxide is an important signaling molecule, this role of ASS is important to vascular physiology. In this role, argininosuccinate synthetase activity is regulated largely by inflammatory cellular signal molecules such as cytokines.

In endothelial cells, it has been shown that ASS expression is increased by laminar shear stress due to pulsative blood flow. Emerging evidence suggests that ASS may also be subject to regulation by phosphorylation at the Ser-328 residue by protein kinase C-α and by nitrosylation at the Cys-132 residue by nitric oxide synthase.

Role in disease

Citrullinemia

Citrullinemia is an inherited autosomal recessive disease. At least 50 mutations that cause type I citrullinemia have been identified in the ASS gene. Most of these mutations substitute one amino acid for another in ASS. These mutations likely affect the structure of the enzyme and its ability to bind to citrulline, aspartate, and other molecules. A few mutations lead to the production of an abnormally short enzyme that cannot effectively play its role in the urea cycle.

Defects in ASS disrupt the third step of the urea cycle, preventing the liver from processing excess nitrogen into urea. As a result, nitrogen (in the form of ammonia) and other byproducts of the urea cycle (such as citrulline) build up in the bloodstream. Ammonia is toxic, particularly to the nervous system. An accumulation of ammonia during the first few days of life leads to poor feeding, vomiting, seizures, and the other signs and symptoms of type I citrullinemia.

Treatment for this defect includes a low-protein diet and dietary supplementation with arginine and phenylacetate. Arginine allows the urea cycle to complete itself, creating the substrates needed to originally fix ammonia. This will lower blood pH. Additionally, phenylacetate reacts with backed-up glutamine, resulting on phenylacetoglutamine, which can be excreted renally.

Cancer biochemistry

A lack of argininosuccinate synthetase expression has been observed in several types of cancer cells, including pancreatic cancer, liver cancer, and melanoma. For example, defects in ASS have been seen in 87% of pancreatic cancers. Cancer cells are therefore unable to synthesize enough arginine for cellular processes and so must rely on dietary arginine. Depletion of plasma arginine using arginine deiminase has been shown to lead to regression of tumours in mice.

See also

• Citrullinemia
• Urea cycle
• Synthetase

References

External links

• GeneReviews/NCBI/NIH/UW entry on Argininosuccinate Synthetase Deficiency; ASS Deficiency; Argininosuccinic Acid Synthetase Deficiency; CTLN1; Citrullinemia, Classic

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

• 1. 低アルドステロン症（4型RTA）の病因、診断、および治療 etiology diagnosis and treatment of hypoaldosteronism type 4 rta
• 2. 血液悪性腫瘍およびリンパ悪性腫瘍の遺伝的異常 genetic abnormalities in hematologic and lymphoid malignancies
• 3. 肝グリコーゲン合成酵素欠損症（糖原病0型） liver glycogen synthase deficiency glycogen storage disease 0
• 4. 尿素サイクル障害：管理 urea cycle disorders management
• 5. 呼気中一酸化窒素の分析 exhaled nitric oxide analysis

English Journal

• Targeting arginine metabolism pathway to treat arginine-dependent cancers.

• Qiu F1, Huang J2, Sui M3.
• Cancer letters.Cancer Lett.2015 Aug 1;364(1):1-7. doi: 10.1016/j.canlet.2015.04.020. Epub 2015 Apr 23.
• The significant disparities in metabolism between tumor and normal cells have inspired the development of metabolism-based anti-tumor therapeutics. Arginine is a semi-essential amino acid because normal cells can not only synthesize arginine de novo but also take up extracellular arginine. Several t
• PMID 25917076

• L-citrulline for protection of endothelial function from ADMA-induced injury in porcine coronary artery.

• Xuan C1, Lun LM1, Zhao JX1, Wang HW1, Wang J2, Ning CP3, Liu Z4, Zhang BB5, He GW6.
• Scientific reports.Sci Rep.2015 Jun 5;5:10987. doi: 10.1038/srep10987.
• Endogenous nitric oxide synthase (eNOS) inhibitor asymmetric dimethylarginine (ADMA) is a cardiovascular risk factor. We tested the hypothesis that L-citrulline may ameliorate the endothelial function altered by ADMA in porcine coronary artery (PCA). Myograph study for vasorelaxation, electrochemica
• PMID 26046576

• Arginine dependence of acute myeloid leukemia blast proliferation: a novel therapeutic target.

• Mussai F1, Egan S2, Higginbotham-Jones J1, Perry T1, Beggs A1, Odintsova E1, Loke J1, Pratt G1, U KP3, Lo A4, Ng M4, Kearns P1, Cheng P3, De Santo C1.
• Blood.Blood.2015 Apr 9;125(15):2386-96. doi: 10.1182/blood-2014-09-600643. Epub 2015 Feb 20.
• Acute myeloid leukemia (AML) is one of the most common acute leukemias in adults and children, yet significant numbers of patients relapse and die of disease. In this study, we identify the dependence of AML blasts on arginine for proliferation. We show that AML blasts constitutively express the arg
• PMID 25710880

Japanese Journal

• Brain nitric oxide production by a proline-rich decapeptide from Bothrops jararaca venom improves baroreflex sensitivity of spontaneously hypertensive rats

• LAMEU Claudiana,PONTIERI Vera,GUERREIRO Juliano R,OLIVEIRA Eduardo F,DA SILVA Carlos Alberto,GIGLIO Joyce M,MELO Robson L,CAMPOS Ruy R,DE CAMARGO Antonio Carlos Martins,ULRICH Henning
• Hypertension research : clinical and experimental : official journal of the Japanese Society of Hypertension 33(12), 1283-1288, 2010-12-01
• NAID 10027682324

• 尿素回路障害 OTC欠損症,ASS欠損症 (小児の治療指針) -- (代謝)

• 高柳 正樹
• 小児科診療 73(-) (866), 490-492, 2010
• NAID 40017118210

Related Links

• Argininosuccinate synthase - Wikipedia, the free encyclopedia

Argininosuccinate synthase or synthetase (ASS) (EC 6.3.4.5) is an enzyme that catalyzes the synthesis of argininosuccinate from citrulline and aspartate. ASS is responsible for the third step of the urea cycle and one of the reactions of the ...

Related Pictures

---

★リンクテーブル★

リンク元	「オルニチン回路」「シトルリン血症」「アルギニノコハク酸合成酵素」
関連記事	「synthase」「argininosuccinate」

「オルニチン回路」

　　[★]

英

ornithine cycle

同

尿素サイクル 尿素回路 urea cycle、クレブス-ヘンゼライト回路 Krebs-Henseleit cycle、オルニチンサイクル

関

オルニチン、尿素

• オルニチン回路に含まれる分子はアミノ酸である：アミノ基とカルボン酸を両方持つもの
• 最終産物である尿素の窒素は、アンモニアとアスパラギン酸に由来する

ミトコンドリア内の反応

1) アンモニア + 炭酸 + 2ATP → ADP + Pi + カルバモイルリン酸 
　　　　　　　　　　　　5)から
　　　　　　　　　　　　↓
2) カルバモイルリン酸 + オルニチン → シトルリン + Pi 
　　　　　　　　　　　　　　　　　　　↓
　　　　　　　　　　　　　　　　　　　3)へ

サイトソルの反応

　　2)から
　　↓
3) シトルリン + アスパラギン酸 + ATP → AMP + ピロリン酸 + アルギニノコハク酸 
4) アルギニノコハク酸 → フマル酸 + アルギニン 
5) アルギニン + 水 → 尿素 + オルニチン 
　　　　　　　　　　　　　　　↓
　　　　　　　　　　　　　　　2)へ

|
ornithine
|
----------mitochondria
|
ornithine
|
|<-carbamoyl phosphate {ornithine transcarbamoylase}
|
citrulline
|
----------mitochondria
|
citrulline
|
|<-aspartate {argininosuccinate synthase}
|
argininosuccinate
| 
|->fumarate {argininosuccinase}
|
arginine
|
|<-H2O
|           {arginase}
|->urea
|
ornithine
|

臨床関連

• 尿素サイクル異常症

「シトルリン血症」

　　[★]

英

citrullinemia

関

シトルリン、argininosuccinate synthase

病因

• I型：アルギニノコハク酸合成酵素遺伝子の異常。
• II型：SLC25A13の遺伝子異常。

遺伝

• (I型)常染色体劣性遺伝

病態

• I型は新生児期に発症
• II型は思春期以降に発症。

検査

• 血中シトルリン濃度上昇
• 血中アンモニア濃度上昇
• その他：フェニルアラニン、メチオニン、ガラクトースが高値で見つかることがある、らしい。だから新生児マススクリーニングで見つかることがある？？？　←　出典不明！！！！！！！！！！！！

参考

• 1. CITRULLINEMIA, CLASSIC - OMIM

http://omim.org/entry/215700

• 2. [charged] Urea cycle disorders: Clinical features and diagnosis - uptodate [1]

「アルギニノコハク酸合成酵素」

　　[★]

英

argininosuccinate synthase AS

同

アルギニノコハク酸シンターゼ

関

アルギニノコハク酸

「synthase」

　　[★]

• n.

• (脱離酵素リアーゼの逆反応である合成方向の反応を指す) シンターゼ, 合成酵素, 付加酵素

関

lyase、synthetase、transferase

「argininosuccinate」

　　[★]

アルギニノコハク酸、アルギノコハク酸

関

argininosuccinic acid

• argininosuccinic acid