Cathepsin D from the liver of the antarctic icefish Chionodraco hamatus exhibits unusual activity and stability at high temperatures1.
Cathepsin D was purified to homogeneity from the liver of Antarctic icefish by anion-exchange chromatography followed by affinity chromatography on concanavalin-A Sepharose. The purified enzyme showed a molecular mass of 40 kDa and displayed optimal activity at pH 3.0 with a synthetic chromogenic substrate. The N-terminal sequence of this proteinase was determined by automated Edman degradation and was used to design a primer for use in reverse-transcriptase polymerase chain reaction. The open reading frame of the cloned cDNA encoded an aspartic proteinase, which contained the experimentally determined N-terminal sequence. The predicted sequence (396 residues) had a high similarity with those of cathepsin D from various vertebrate sources, but was considerably different from that of nothepsin, a distinct aspartic proteinase described previously from Antarctic fish [1]. Determination of kinetic parameters for substrate hydrolysis showed that, at temperatures between 8 and 50 degrees C, the icefish cathepsin D had a higher specificity constant (kcat/Km) than human cathepsin D. The stability of both enzymes was measured at 50 degrees C and half-lives of 55 and 3 min were derived for icefish and human cathepsin D, respectively.
Capasso
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CNR Institute of Protein Biochemistry and Enzymology, via Marconi, 10-I 80125, Naples, Italy.
Lees
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Capasso
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Scudiero
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Carginale
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Kille
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Kay
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Parisi
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D000595:Amino Acid Sequence; D000818:Animals; D000864:Antarctic Regions; D001483:Base Sequence; D002402:Cathepsin D / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry; D004789:Enzyme Activation; D004795:Enzyme Stability; D005399:Fishes / Q000378:metabolism*; D007558:Italy; D008099:Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D013696:Temperature
D018076:DNA, Complementary; D002402:Cathepsin D