Astacin

Title: Astacin
CAS Registry Number: 514-76-1
CAS Name: b,b-Carotene-3,3¢,4,4¢-tetrone
Additional Names: 3,4,3¢,4¢-tetraketo-b-carotene; 3,3¢-dihydroxy-2,3,2¢,3¢-tetradehydro-b,b-carotene-4,4¢-dione; astacene
Molecular Formula: C40H48O4
Molecular Weight: 592.81
Percent Composition: C 81.04%, H 8.16%, O 10.80%
Literature References: Red carotenoid pigment isolated from biological material originating from crustacea, algae, sponges, protozoa, fish and reptiles. Small amounts were isolated from the fat of mammals (whales, Balaenoptera musculus). Occurs together with astaxanthin from which it is formed by autoxidation. Appears to be an artifact rather than a natural product. Isoln from lobster shells: Kuhn, Lederer, Ber. 66, 488 (1933). Structure: Karrer et al., Helv. Chim. Acta 17, 412, 745 (1934); 18, 96 (1935); 19, 479 (1936). Total synthesis: J. B. Davis, B. C. L. Weedon, Proc. Chem. Soc. London 1960, 182; E. Widmer et al., Helv. Chim. Acta 65, 671 (1982). Prepn by autoxidation of canthaxanthin: R. D. G. Cooper et al., J. Chem. Soc. Perkin Trans. 1 1975, 2195.
Properties: Purple needles or leaflets with metallic luster, sometimes bent into sickle shape, esp when crystallized from pyridine + water, mp 240-243° (slow heating in evac tube, Karrer), mp 228° (Kuhn). Absorption max (pyridine): 500 nm. Practically insol in water; freely sol in chloroform, pyridine, dioxane, carbon disulfide and dil aq alkali; slightly sol in benzene, ethyl acetate, glacial acetic acid; nearly insol in ether, petr ether, methanol.
Melting point: mp 240-243° (slow heating in evac tube, Karrer); mp 228° (Kuhn)
Absorption maximum: Absorption max (pyridine): 500 nm
Derivative Type: Diacetate
Molecular Formula: C44H52O6
Molecular Weight: 676.88
Percent Composition: C 78.07%, H 7.74%, O 14.18%
Properties: Black to violet needles from pyridine + water, dec 235°.
Derivative Type: Dipalmitate (astacein)
Molecular Formula: C72H108O6
Molecular Weight: 1069.62
Percent Composition: C 80.85%, H 10.18%, O 8.97%
Properties: Almost square red leaflets from petr ether, mp 121°.
Melting point: mp 121°
Astemizole Asulam Atenolol Atevirdine Athamantin

Astacin
PDB 1qjj EBI.jpg
structure of astacin with a hydroxamic acid inhibitor
Identifiers
Symbol Astacin
Pfam PF01400
Pfam clan CL0126
InterPro IPR001506
PROSITE PDOC00129
MEROPS M12
SCOP 1ast
SUPERFAMILY 1ast
astacin
Identifiers
EC number 3.4.24.21
CAS number 143179-21-9
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

In molecular biology, astacin is a family of metallopeptidases. These metallopeptidases belong to the MEROPS peptidase family M12, subfamily M12A (astacin family, clan MA(M)). The protein fold of the peptidase domain for members of this family resembles that of thermolysin, the type example for clan MA and the predicted active site residues for members of this family and thermolysin occur in the motif HEXXH.[1]

The astacin family of metalloendopeptidases (EC 3.4.24.21) encompasses a range of proteins found in hydra to humans, in mature and developmental systems.[2] Their functions include activation of growth factors, degradation of polypeptides, and processing of extracellular proteins.[2] The proteins are synthesised with N-terminal signal and pro-enzyme sequences, and many contain multiple domains C-terminal to the protease domain. They are either secreted from cells, or are associated with the plasma membrane.

The astacin molecule adopts a kidney shape, with a deep active-site cleft between its N- and C-terminal domains.[3] The zinc ion, which lies at the bottom of the cleft, exhibits a unique penta-coordinated mode of binding, involving 3 histidine residues, a tyrosine and a water molecule (which is also bound to the carboxylate side chain of Glu93).[3] The N-terminal domain comprises 2 alpha-helices and a 5-stranded beta-sheet. The overall topology of this domain is shared by the archetypal zinc-endopeptidase thermolysin. Astacin protease domains also share common features with serralysins, matrix metalloendopeptidases, and snake venom proteases; they cleave peptide bonds in polypeptides such as insulin B chain and bradykinin, and in proteins such as casein and gelatin; and they have arylamidase activity.[2]