Regulation of stromal sedoheptulose 1,7-bisphosphatase activity by pH and Mg2+ concentration.

I E Woodrow,D J Murphy,E Latzko

doi:10.1016/s0021-9258(17)43164-4

Abstract

A scheme is proposed for the regulation of stromal sedoheptulose 1,7-bisphosphatase activity which enlarges upon a previously elaborated mechanism (Woodrow, I.E., and Walker, D.A. (1983) Biochim. Biophys. Acta 722, 508-516). The latter involves oxidized (inactive) and reduced (active) enzyme forms. Both the free enzymes and the enzyme-substrate complexes undergo slow oxidation/reduction. This study examines the behavior of the system under pH and Mg2+ concentration regimes that are likely to occur in the chloroplast stroma. The control of enzyme activity by pH can be described in terms of each free enzyme and enzyme-substrate complex existing in protonated and nonprotonated forms. The molecular dissociation constants for each protonation reaction were calculated from kinetic data. Mg2+ concentration changes modulate these constants. Under conditions that are likely to obtain in the stroma in the dark, the model predicts that approximately 99.1% of the enzyme will be in the inactive forms. Such inactivation is important since it would prevent the reductive pentose phosphate pathway from operating in darkness.

Highlights

A scheme is proposed for the regulation of stromal roplasts caused an inhibition of CO, fixation and an increase sedoheptulose 1,7-bisphosphatase activity which en- in both the fructose 1,6-bisphosphateand sedoheptulose1,?
This effected a decline in the carbon flux and an increase in the sedoheptulose 1,7-bisphosphate and fructose 1,6-bisphosphatelevels which were suggestedto
This mechanism is based upononepreviouslysuggested to account for the effect of reductant, oxidant, and substrate on enzyme activity (Woodrow and Walker, 1983; Woodrowet al., 1983)

Summary

Introduction

A scheme is proposed for the regulation of stromal roplasts caused an inhibition of CO, fixation and an increase sedoheptulose 1,7-bisphosphatase activity which en- in both the fructose 1,6-bisphosphateand sedoheptulose1,?-. Et al, 1966; Purczeld et al, 1978; Enser and Heber, 1980; Acta 722, 508-516) The latter involves oxidized (in- Flugge et al, 1980). The rise in these metabolite levels and active) and reduced (active) enzyme forms. Both the the concomitant decline in the carbon flux was interpreted to free enzymesandtheenzyme-substratecomplexes mean that the activities of fructose bisphosphatase and seusepinccntnohHnoaenlzndnosyccpertaemtrrsohnngopefetotborl-obaserasnuseltedotahibaowetasscnesttvhdocrrirroxaopeifmitrbgrodeooieraamftdmc.totoiehnTosimsn.neahtptT/sherityloeaheescnrtdextomeeaurnxmmrecstieatrsouioctoolintlfelnniicdokeog.uneeaTflrilcanwhyehfrniresptzredosrpyeeitoosmHucetcsadnoaocelnaczyuccytniarueaimdtvxliteaniiaedotMtmtyenhaad8b-nency+ddon-fbtdtChheeoOreeTlhiso,eehe7ffvpe-iMe8etxudntaglrzttZoraioya+sonnmebnsigoef.ebeensiersslapope(nlfchDadtpoyritrslilhcaopeaathyosltalia,nygtnsancudsoianefVmcidcareepoarrreesnnsntcosstorenhaonn,etldees1iidt9tthii6ifnyvoo5lenr;laiBsbtkmoyaooifritapbdinHdcemgeorcuecetlhtnhmineataebiln.nrrr,gatagr1etnae9spen7Hiosni4s-f,; from kinetic data. Mg“+ concentration changesmodu- Hind et al, 1974; Krause, 1974; Krause, 1977). Such inactivationis important since it 1974;Chow et al, 1976). This effected a decline in the carbon flux and an increase in the sedoheptulose 1,7-bisphosphate and fructose 1,6-bisphosphatelevels which were suggestedto

Methods

Results

Conclusion