Relationship between NH sub 4 sup + assimilation rate and in vivo phosphoenolpyruvate carboxylase activity

Journal Article · Sat Sep 01 00:00:00 EDT 1990 · Plant Physiology; (USA)

DOI:https://doi.org/10.1104/pp.94.1.284· OSTI ID:5962101

Vanlerberghe, G C; Schuller, K A; Smith, R G; Feil, R; Plaxton, W C; Turpin, D H ^[1]

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1. Queen's Univ., Kingston, Ontario (Canada)

The rate of NH{sub 4}{sup +} assimilation by N-limited Selenastrum minutum (Naeg.) Collins cells in the dark was set as an independent variable and the relationship between NH{sub 4}{sup +} assimilation rate and in vivo activity of phosphoenolpyruvate carboxylase (PEPC) was determined. In vivo activity of PEPC was measured by following the incorporation of H{sup 14}CO{sub 3}{sup {minus}} into acid stable products. A linear relationship of 0.3 moles C fixed via PEPC per mole N assimilated was observed. This value agrees extremely well with the PEPC requirement for the synthesis of the amino acids found in total cellular protein. Determinations of metabolite levels in vivo at different rates of N assimilation indicated that the known metabolite effectors of S. minutum PEPC in vitro (KA Schuller, WC Plaxton, DH Turpin, (1990) Plant Physiol 93: 1303-1311) are important regulators of this enzyme during N assimilation. As PEPC activity increased in response to increasing rates of N assimilation, there was a corresponding decline in the level of PEPC inhibitors (2-oxoglutarate, malate), an increase in the level of PEPC activators (glutamine, dihydroxyacetone phosphate), and an increase in the Gln/Glu ratio. Treatment of N-limited cells with azaserine caused an increase in the Gln/Glu ratio resulting in increased PEPC activity in the absence of N assimilation. We suggest glutamate and glutamine play a key role in regulating the anaplerotic function of PEPC in this C{sub 3} organism.

• OSTI ID: 5962101
• Journal Information: Plant Physiology; (USA), Vol. 94:1; ISSN 0032-0889
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
AMMONIA
UPTAKE
CARBOXYLASE
BIOCHEMICAL REACTION KINETICS
CARBON 14 COMPOUNDS
CHLOROPHYCOTA
IN VIVO
PYRUVIC ACID
TRACER TECHNIQUES
ALGAE
CARBON-CARBON LYASES
CARBOXY-LYASES
CARBOXYLIC ACIDS
ENZYMES
HYDRIDES
HYDROGEN COMPOUNDS
ISOTOPE APPLICATIONS
KETO ACIDS
KINETICS
LABELLED COMPOUNDS
LYASES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
PLANTS
REACTION KINETICS
550201* - Biochemistry- Tracer Techniques