Diurnal changes in phosphoenolpyruvate carboxylase and pyruvate,orthophosphate dikinase properties in the natural environment: interplay of light and temperature in a C4 thermophile

1990 ◽  
Vol 80 (4) ◽  
pp. 593-597 ◽  
Author(s):  
George Grammatikopoulos ◽  
Yiannis Manetas
Keyword(s):  
Natural Environment ◽  
Phosphoenolpyruvate Carboxylase ◽  
Diurnal Changes ◽  
Pyruvate Orthophosphate Dikinase ◽  
Orthophosphate Dikinase

Phosphoenolpyruvate carboxylase mediated carbon flow in a cyanobacterium

1988 ◽  
Vol 66 (2) ◽  
pp. 93-99 ◽  
Author(s):  
George W. Owttrim ◽  
Brian Colman
Keyword(s):  
Phosphoenolpyruvate Carboxylase ◽  
Protein Production ◽  
Carbon Fixation ◽  
Fixed Carbon ◽  
Free System ◽  
Pyruvate Orthophosphate Dikinase ◽  
Orthophosphate Dikinase ◽  
Phosphoglyceric Acid ◽  
A Cell

The source of the substrate phosphoenolpyruvate (PEP) for phosphoenolpyruvate carboxylase (PEP-case) activity in the cyanobacterium Coccochloris peniocystis has been investigated, as well as possible sinks for this carbon. PEP was not produced by pyruvate orthophosphate dikinase, as this activity was not detectable in cell-free lysates. PEP is supplied from photosynthetically or glycolytically produced 3-phosphoglyceric acid (3-PGA), as carbon was observed to flow from 3-PGA to C4 acids in a cell-free system. This indicates PEP-case activity is dependent on photosynthetically fixed carbon and thus two separate carbon fixation reactions occur in the cell in the light. Estimates of the in vivo concentrations of various metabolites indicates that neither substrate nor inhibitor concentrations limit enzyme activity in vivo. Thus PEP-case activity in vivo appears to be limited by the supply of PEP and is, therefore, high in the light and low in the dark. The nitrogen storage product cyanophycin was identified as one sink for carbon fixed by PEP-case. As a culture aged, cyanophycin production increased, while chlorophyll and protein production decreased.

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