REGULATION OF CARBON ASSIMILATION IN CHLOROPLASTS: I. ACTIVATION OF RIBULOSE 1,5-BISPHOSPHATE CARBOXYLASE/OXYGENASE; II. CONTROL OF STARCH METABOLISM

Persistent Link:
http://hdl.handle.net/10150/290525
Title:
REGULATION OF CARBON ASSIMILATION IN CHLOROPLASTS: I. ACTIVATION OF RIBULOSE 1,5-BISPHOSPHATE CARBOXYLASE/OXYGENASE; II. CONTROL OF STARCH METABOLISM
Author:
Hatch, Alan Lorenzo
Issue Date:
1980
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Ribulose 1,5-biphosphate carboxylase/oxygenase is activated by incubation with CO₂ and Mg²⁺. Several compounds are known to mediate this CO₂ dependent activation, including several chloroplast metabolites. A search, based on structural similarities to known activators, encountered more than twenty previously unreported effectors. Activators appear to share several common characteristics, including two anionic groups which usually occupy terminal positions on the molecule. Terminal groups on activators include carboxylate, phosphate, phosphonate, and sulfonate. Activators which do not have at least one phosphate or phosphonate terminal group have a hydroxyl or carboxyl containing side chain. Positive effectors change the response of the carboxylase by allowing activation at lower levels of CO₂ and/or Mg²⁺, and at lower pH values. Higher CO₂ concentrations also allow activation at lower pH values. The ratio between the carboxylase and oxygenase functions of this enzyme at air levels of CO₂ and O₂ does not change with effector induced changes in enzyme activity, suggesting that they share the same active site. There is an apparent difference in the response of the enzyme before and after purification to incubation in phosphate, and to inhibition by the substrate ribulose 1,5-biphosphate. These observations suggest that the isolated protein is different from the native enzyme. Several carboxylase activators are taken up by isolated chloroplasts in an exchange for phosphate catalyzed by the phosphate translocator. Included in this group is phosphonopropionate, a non-metabolized analogue of phosphoglycerate. Addition of this effector to chloroplasts under conditions of photosynthesis results in increased carboxylase activity, but a decrease in both ribulose 1,5-biphosphate levels and CO₂ fixation. There is a slow leakage of phosphate from isolated chloroplasts at room temperature. This leakage does not occur during illumination, nor at ice temperature, but increases with increasing hydroxide ion over physiological pH values. This slow leakage is probably an artifact of chloroplast isolation procedures. In isolated chloroplasts, phosphate levels appear to control the partition of photosynthate between starch formation and sugar phosphate export. During periods of net accumulation of starch in the chloroplast, there is concomitant degradation occurring, such that the accumulation of label into the starch fraction may not reflect the actual rate of starch synthesis.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Chloroplasts.; Ribulosebisphosphate carboxylase.; Starch -- Metabolism.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleREGULATION OF CARBON ASSIMILATION IN CHLOROPLASTS: I. ACTIVATION OF RIBULOSE 1,5-BISPHOSPHATE CARBOXYLASE/OXYGENASE; II. CONTROL OF STARCH METABOLISMen_US
dc.creatorHatch, Alan Lorenzoen_US
dc.contributor.authorHatch, Alan Lorenzoen_US
dc.date.issued1980en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractRibulose 1,5-biphosphate carboxylase/oxygenase is activated by incubation with CO₂ and Mg²⁺. Several compounds are known to mediate this CO₂ dependent activation, including several chloroplast metabolites. A search, based on structural similarities to known activators, encountered more than twenty previously unreported effectors. Activators appear to share several common characteristics, including two anionic groups which usually occupy terminal positions on the molecule. Terminal groups on activators include carboxylate, phosphate, phosphonate, and sulfonate. Activators which do not have at least one phosphate or phosphonate terminal group have a hydroxyl or carboxyl containing side chain. Positive effectors change the response of the carboxylase by allowing activation at lower levels of CO₂ and/or Mg²⁺, and at lower pH values. Higher CO₂ concentrations also allow activation at lower pH values. The ratio between the carboxylase and oxygenase functions of this enzyme at air levels of CO₂ and O₂ does not change with effector induced changes in enzyme activity, suggesting that they share the same active site. There is an apparent difference in the response of the enzyme before and after purification to incubation in phosphate, and to inhibition by the substrate ribulose 1,5-biphosphate. These observations suggest that the isolated protein is different from the native enzyme. Several carboxylase activators are taken up by isolated chloroplasts in an exchange for phosphate catalyzed by the phosphate translocator. Included in this group is phosphonopropionate, a non-metabolized analogue of phosphoglycerate. Addition of this effector to chloroplasts under conditions of photosynthesis results in increased carboxylase activity, but a decrease in both ribulose 1,5-biphosphate levels and CO₂ fixation. There is a slow leakage of phosphate from isolated chloroplasts at room temperature. This leakage does not occur during illumination, nor at ice temperature, but increases with increasing hydroxide ion over physiological pH values. This slow leakage is probably an artifact of chloroplast isolation procedures. In isolated chloroplasts, phosphate levels appear to control the partition of photosynthate between starch formation and sugar phosphate export. During periods of net accumulation of starch in the chloroplast, there is concomitant degradation occurring, such that the accumulation of label into the starch fraction may not reflect the actual rate of starch synthesis.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectChloroplasts.en_US
dc.subjectRibulosebisphosphate carboxylase.en_US
dc.subjectStarch -- Metabolism.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.identifier.proquest8017754en_US
dc.identifier.oclc8714025en_US
dc.identifier.bibrecord.b13918692en_US
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