Alanine aminotransferase in Leptosphaeria michotii. Isolation, properties and cyclic variations of its activity in relation to polypeptide level |
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Authors: | A M Abou-Zeid S Jerebzoff S Jerebzoff-Quintin |
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Institution: | Dept of Botany, Univ. of Tanta, Egypt;;Biorhythm Lab., Plant Physiology Center and URA 241, CNRS, P. Sabatier Univ., 118 route de Narbonne, F-31062 Toulouse Cedex, France. |
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Abstract: | Alanine aminotransferase (EC 2.6.1.2) was obtained from the fungus Leptosphaeria michotii (West) Sacc, and enriched 714-fold by a 5-step purification procedure as a dimer of Mr 110000, associated with a polypeptide of Mr 25000. Its isoelectric point was 5.25. The enzyme was active from pH 3.5 to 9.5 with a maximum at pH 7.5. Its specific activity was 6000 nkat (mg protein)?1; the Km was 6.85 m M for L-alanine and 0.2 m M for 2-oxoglutarate. The enzyme did not show any detectable activity in the presence of L-aspartate, cysteine sulfinate, α-aminobutyrate or cyclic amino acids as substrates. It did not express alanine:glyoxylate aminotransferase activity. Alanine aminotransferase in L. michotii has previously been shown to have an activity rhythm in constant temperature and darkness. The enzyme level was quantified along the activity rhythm by enzyme-linked immunosorbent assay (ELISA), using a monospecific polyclonal antibody against the purified enzyme. The cyclic variations of alanine aminotransferase activity were correlated with cyclic variations in the enzyme level. |
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Keywords: | Alanine aminotransferase Leptosphaeria michotii rhythm |
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