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Plant and Cell Physiology, 1995, Vol. 36, No. 8 1459-1470
© 1995

Purification, Properties and Phosphorylation of Anaerobically Induced Enolase in Echinochloa phyllopogon and E. crus-pavonis

Cesar V. Mujer1, Theodore C. Fox1, Adrienne S. Williams1, David L. Andrews1, Robert A. Kennedy2 and Mary E. Rumpho1,3

1 Department of Horticultural Sciences, Texas A & M University College Station, TX 77843, U.S.A.
2 Department of Biology, Texas A & M University College Station, TX 77843, U.S.A.

3To whom correspondence should be addressed; Fax 1-409-845-0627.

Enolase (2-phospho-D-glycerate hydrolyase, EC 4.2.1.11 [EC] ) activity is differentially induced by anoxia in the flood-tolerant species E. phyllopogon (Stev.) Koss and the flood-intolerant species E. crus-pavonis (H.B.K.) Schult. To examine the regulation of enolase at the protein level, we purified the enzyme from both species to near homogeneity and compared their physico-chemical and catalytic properties. Enolase purified from E. phyllopogon exhibits optimal activity at pH 7.0, a Km of 80 µM for 2-PGA, a Q10 of 1.97 and an Ea of 12.3 kcal mol-1. Similarly, enolase from E. crus-pavonis exhibits optimal activity at pH 7.0, a Km of 50 µM for 2-PGA, a Q10 of 2.04 and an Ea of 12.9 kcal mol-1. The enzyme from both species is thermostable (100% active after 15 min, 50°C) and is a homodimer of 52.5 kDa subunits as resolved by SDS-PAGE and immunoblotting. E. phyllopogon enolase was phosphorylated in vitro using either [{gamma}-32P]ATP or [{gamma}-32P]GTP; however, enolase activity was neither stimulated nor inhibited by phosphorylation. Furthermore, addition of alkaline phosphatase had no effect on enolase activity. These findings suggest that factors other than phosphorylation regulate enolase activity under anaerobic stress. Likewise, since the properties of purified enolase from the two species are almost identical, the differential induction of activity under anoxia cannot be ascribed to possible differences in catalytic functions between the two enzymes.

(Received May 15, 1995; Accepted August 24, 1995)
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S. K. Lal, C. Lee, and M. M. Sachs
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