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Interaction of acetyl phosphate and carbamyl phosphate with plant phosphoenolpyruvate carboxylase.

ABSTRACT: Acetyl phosphate produced an increase in the maximum velocity (Vmax. for the carboxylation of phosphoenolpyruvate catalysed by phosphoenolpyruvate carboxylase. The limiting Vmax. was 22.2 mumol X min-1 X mg-1 (185% of the value without acetyl phosphate). This compound also decreased the Km for phosphoenolpyruvate to 0.18 mM. The apparent activation constants for acetyl phosphate were 1.6 mM and 0.62 mM in the presence of 0.5 and 4 mM-phosphoenolpyruvate respectively. Carbamyl phosphate produced an increase in Vmax. and Km for phosphoenolpyruvate. The variation of Vmax./Km with carbamyl phosphate concentration could be described by a model in which this compound interacts with the carboxylase at two different types of sites: an allosteric activator site(s) and the substrate-binding site(s). Carbamyl phosphate was hydrolysed by the action of phosphoenolpyruvate carboxylase. The hydrolysis produced Pi and NH4+ in a 1:1 relationship. Values of Vmax. and Km were 0.11 +/- 0.01 mumol of Pi X min-1 X mg-1 and 1.4 +/- 0.1 mM, respectively, in the presence of 10 mM-NaHCO3. If HCO3- was not added, these values were 0.075 +/- 0.014 mumol of Pi X min-1 X mg-1 and 0.76 +/- 0.06 mM. Vmax./Km showed no variation between pH 6.5 and 8.5. The reaction required Mg2+; the activation constants were 0.77 and 0.31 mM at pH 6.5 and 8.5 respectively. Presumably, carbamyl phosphate is hydrolysed by phosphoenolpyruvate carboxylase by a reaction the mechanism of which is related to that of the carboxylation of phosphoenolpyruvate.

SUBMITTER: Gonzalez DH

PROVIDER: S-EPMC1147594 | biostudies-other | 1987 Jan

REPOSITORIES: biostudies-other

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Project description:Phosphoenolpyruvate carboxylase (PEPC) is an important enzyme in plants, which regulates carbon flow through the TCA cycle and controls protein and oil biosynthesis. Although it is important, there is little research on PEPC in cotton, the most important fiber crop in the world. In this study, a total of 125 PEPCs were identified in 15 Gossypium genomes. All PEPC genes in cotton are divided into six groups and each group generally contains one PEPC member in each diploid cotton and two in each tetraploid cotton. This suggests that PEPC genes already existed in cotton before their divergence. There are additional PEPC sub-groups in other plant species, suggesting the different evolution and natural selection during different plant evolution. PEPC genes were independently evolved in each cotton sub-genome. During cotton domestication and evolution, certain PEPC genes were lost and new ones were born to face the new environmental changes and human being needs. The comprehensive analysis of collinearity events and selection pressure shows that genome-wide duplication and fragment duplication are the main methods for the expansion of the PEPC family, and they continue to undergo purification selection during the evolutionary process. PEPC genes were widely expressed with temporal and spatial patterns. The expression patterns of PEPC genes were similar in G. hirsutum and G. barbadense with a slight difference. PEPC2A and 2D were highly expressed in cotton reproductive tissues, including ovule and fiber at all tested developmental stages in both cultivated cottons. However, PEPC1A and 1D were dominantly expressed in vegetative tissues. Abiotic stress also induced the aberrant expression of PEPC genes, in which PEPC1 was induced by both chilling and salinity stresses while PEPC5 was induced by chilling and drought stresses. Each pair (A and D) of PEPC genes showed the similar response to cotton development and different abiotic stress, suggesting the similar function of these PEPCs no matter their origination from A or D sub-genome. However, some divergence was also observed among their origination, such as PEPC5D was induced but PEPC5A was inhibited in G. barbadense during drought treatment, suggesting that a different organized PEPC gene may evolve different functions during cotton evolution. During cotton polyploidization, the homologues genes may refunction and play different roles in different situations.

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Interaction of acetyl phosphate and carbamyl phosphate with plant phosphoenolpyruvate carboxylase.

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