Status of the substrate binding sites of ribulose bisphosphate carboxylase as determined with 2-C-carboxyarabinitol 1,5-bisphosphate. [Spinacia oleracea]

Journal Article · Tue May 01 04:00:00 EDT 1990 · Plant Physiology; (USA)

DOI:https://doi.org/10.1104/pp.93.1.244· OSTI ID:5924472

Zhu, Genhai; Jensen, R G ^[1]

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1. Univ. of Arizona, Tucson (USA)

The properties of the tight and specific binding of 2-C-carboxy-D-arabinitol 1,5-bisphosphate (CABP), which occurs only to reaction sites of ribulose 1,5-bisphosphate carboxylase (Rubisco) that are activated by CO{sub 2} and Mg{sup 2+}, were studied. With fully active purified spinach (Spinacia oleracea) Rubisco the rate of tight binding of ({sup 14}C)CABP fit a multiple exponential rate equation with half of the sites binding with a rate constant of 40 per minute and the second half of the sites binding at 3.2 per minute. This suggests that after CABP binds to one site of a dimer of Rubisco large subunits, binding to the second site is considerably slower, indicating negative cooperativity as previously reported. The rate of CABP binding to partially activated Rubisco was complete within 2 to 5 minutes, with slower binding to inactive sites as they formed the carbamate and bound Mg{sup 2+}. Addition of ({sup 14}C)CABP and EDTA stopped binding of Mg{sup 2+} and allowed tight binding of the radiolabel only to sites which were CO{sub 2}/Mg{sup 2+}-activated at that moment. The rate of CO{sub 2} fixation was proportional to the CO{sub 2}/Mg{sup 2+}-activated sites. During light-dependent CO{sub 2} fixation with isolated spinach chloroplasts, the amount of carbamylation was proportional to Rubisco activity either initially upon lysis of the plastids or following total activation with Mg{sup 2+} and CO{sub 2}. Lysis of chloroplasts in media with ({sup 14}C)CABP plus EDTA estimated those carbamylated sites having Mg{sup 2+}. The loss of Rubisco activation during illumination was partially due to the lack of Mg{sup 2+} to stabilize the carbamylated sites.

• OSTI ID: 5924472
• Journal Information: Plant Physiology; (USA), Journal Name: Plant Physiology; (USA) Vol. 93:1; ISSN 0032-0889; ISSN PLPHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH METALS
BIOCHEMICAL REACTION KINETICS
CARBON 14 COMPOUNDS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON DIOXIDE FIXATION
CARBON OXIDES
CARBON-CARBON LYASES
CHALCOGENIDES
ELEMENTS
ENZYMES
FOOD
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
LYASES
MAGNESIUM
MAGNOLIOPHYTA
MAGNOLIOPSIDA
METALS
OXIDES
OXYGEN COMPOUNDS
PLANTS
REACTION KINETICS
SPINACH
TRACER TECHNIQUES
VEGETABLES