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Characterization of an l ‐aspartate aminotransferase activity in Chlamydomonas reinhardtii
Author(s) -
MuñozBlanco Juan,
LainGuelbenzu Blanca,
Torres Jacobo Cárdenas
Publication year - 1988
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1988.tb01999.x
Subject(s) - chlamydomonas reinhardtii , biochemistry , enzyme , chlamydomonas , intracellular , glutamate receptor , pyridoxal 5 phosphate , biology , chemistry , pyridoxal , gene , receptor , mutant
The isolation and characterization of an l ‐aspartate aminotransferase (AAT) activity (EC 2.6.1.1) in the unicellular green alga Chlamydomonas reinhardtii 6145c are reported for the first time. The enzyme transaminates aspartate with the 2‐oxoglutarate‐glutamate system, and exhibits maximum aminotransferase activity at pH 7.8 and 37°C. It has an Mr of 138 kDa, contains pyridoxal 5′‐phosphate, and has a K m apparent for oxalacetate of 0.55 m M and exhibits positive co‐operativity with l ‐aspartate with an S 0.5 of 2.53 m M and a Hill coefficient of 1.57. In vivo, activity levels were affected by the carbon and nitrogen sources and by the change in the dark‐light conditions. All these responses are interpreted in terms of a possible physiological regulation of AAT activity to keep the intracellular pools of glutamate and aspartate within margins compatible with environmental fluctuations.