Catalytic activity of aspartate aminotransferase microcrystals

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Catalytic activity of non-cross-linked microcrystals of aspartate aminotransferase in poly(ethylene glycol).

The molar activity of crystalline mitochondrial aspartate aminotransferase is decreased to 10% of that of the enzyme in solution. The activity was measured in suspensions of non-cross-linked microcrystals (average dimensions 22 microns X 5 microns X 0.8 microns) in 30% (w/v) poly(ethylene glycol). Kinetic tests ruled out the possibility that diffusion of the substrate in the crystals is rate-li...

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The enzyme mitochondrial aspartate aminotransferase from beef liver is a dimer of identical subunits. The enzymatic activity of the resolved enzyme is restored upon addition of the cofactor pyridoxal 5-phosphate. The binding of 1 molecule of cofactor restores 50% of the original enzymatic activity, whereas the binding of a 2nd molecule of cofactor brings about more than 95% recovery of the cata...

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Catalytic activity in crystals of mitochondrial aspartate aminotransferase as detected by microspectrophotometry.

Triclinic single crystals of mitochondrial aspartate aminotransferase from chicken were examined by microspectrophotometry using nonpolarized light. The crystalline enzyme shows the same protein and coenzyme absorption bands in the 250 to 500 nm region as the enzyme in solution. The spectrum of the pyridoxal form (A,,, 355 nm) changes into that of the pyridoxamine form (X,,, 333 nm) when excess...

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Unexplained High Activity of Aspartate Aminotransferase in an Asymptomatic Pediatric Patient

Elevated enzyme activities in plasma may at times be attributed to the presence of macro-enzymes. The macro-enzymes are often serum enzymes in complex with immunoglobulins, resulting in a greater molecular mass that cannot be filtered by renal glomeruli and are, hence, retained in the plasma. The aspartate aminotransferase (AST) can exist as a macro-enzyme, although it has been rarely reported....

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The cofactor pyridoxal 5’-phosphate bound through an aldimine linkage to lysine residues of the enzyme aspartate amiuotransferase is very stable to irradiation with light of 420 nm. The catalytic function of the enzyme exposed to light absorbed by the cofactor remains unaffected, indicating that pyridoxal 5’-phosphate is not an efficient active site photosensitizer for this aminotransferase. Th...

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ژورنال

عنوان ژورنال: Biopolymers and Cell

سال: 1986

ISSN: 0233-7657,1993-6842

DOI: 10.7124/bc.00019e