The Subunit Structure of Porcine Ornithine Aminotransferase and Mechanism of Proteolytic Modification of its Putative Precursors in Mitochondria

Tsai, Hui Lien; Lünsdorf, Heinrich; Floßdorf, Josef; Tsai, Jane H. J.

doi:10.1007/978-3-0348-9308-4_9

Cited by 1 publication

(7 citation statements)

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“…pyridoxal-P at pH 7.0 (Tsai et al, 1987). Under such conditions, the enzyme represents the active holo-form.…”

Section: Resultsmentioning

confidence: 99%

“…Even mild cross-linking of the enzyme at high protein concentrations with glutardialdehyde (Josephs et al, 1973) or suberimidate did not help to obtain appropriate polymers (data not shown). Instead, Tsai et al (1987) proved, for the porcine OAT, that the molecular mass of this enzyme was dependent simply on the rotor speed during sedimentation equilibrium runs. Thus, a molecular mass of 350kDa was found at low speed (3200rpm) which changed to 260kDa at higher speed (5600rpm).…”

Section: Resultsmentioning

confidence: 99%

“…rat liver and kidney (Matsuzawa et al, 1968;Sanada et al, 1970;Sanada et al, 1976;John and Fowler, 1985;Leah et al, 1987), pig kidney (Jenkins and Tsai, 1970;Tsai et al, 1987), human liver (Ohura et al, 1982;Leah et al, 1987), and tobacco hornworm larva (Rosenthal and Dahlman, 1990). A prokaryotic aminotransferase, the o-aminoacid :pyruvate aminotransferase from Pseudomonas spec.…”

Section: Resultsmentioning

confidence: 99%

“…Negative staining of highly purified OAT enzyme particles has been performed with 3% (masskol.) uranylacetate, pH 4.5, following the procedure of Valentine et al (1968). The conventional electron microscopic analysis was carried out with Zeiss EM 1 OB and electron spectroscopic imaging (ESI) was performed with the Zeiss CEM 902 as described by Braun et al (1991).…”

Section: Methodsmentioning

confidence: 99%

“…Ornithine aminotransferase (OAT) is a pyridoxal-5'-phosphate-(pyridoxal-P)-dependent enzyme which is located in the mitochondria1 matrix (Tsai et al, 1987;Peraino and Pitot, 1963). The enzyme catalyzes a reversible transamination reaction between a-oxoglutaric acid and L-ornithine, in which the 6-NH2, rather than the a-NH, group of L-ornithine serves as the amino donor.…”

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confidence: 99%

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High‐resolution Electron Microscopic Studies on the Quaternary Structure of Ornithine Aminotransferase from Pig Kidney

Lünsdorf

Hecht

Tsai

1994

European Journal of Biochemistry

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The ornithine aminotransferase (OAT) from pig kidney has been studied on the basis of highresolution electron microscopy and the morphological appearance of the apoenzyme and holoenzyme have been examined. The quaternary structure of the OAT molecules in the presence of 5 mM pyridoxal 5'-phosphate could be established. The enzyme molecule appears to be built up of two morphological units, called M1. The native holoenzyme, termed morphological unit M2, measures . 10.9 nm in length and 5.8 nm in width and its molecular mass is approximately 168 kDa, based on electron microscopical calculations. Since the enzyme is composed of only one type of 45-kDa subunit, the holoenzyme is a homotetramer. Each M1 is composed of two subunits and, as seen in top-view projection, has an oval to triangular shape. Upon tilting to 40" the triangular shape changes into three distinct centers of mass. This morphological differentiation reflects the inner organization of M1, i.e. the shape of the individual subunit deviates from strictly globular proteins. This observation is compatible with the notion that the 45-kDa subunit consists of one large and one small domain. By tilting to 40", both large domains in M1 represent two of the three centers of mass, while the third center of mass is attributed to the superposition of both small domains. Thus, the four domains of both subunits in M1, in accordance with the triangular top-view projection, are quasi-tetrahedrally arranged. Since the change in shape of M1 upon tilting is only obvious in one of the two halves of the native OAT, it suggests that both morphological units of M2 are oriented asymmetrically relative to one another.

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“…pyridoxal-P at pH 7.0 (Tsai et al, 1987). Under such conditions, the enzyme represents the active holo-form.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%