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. 1979 Mar;63(3):531–535. doi: 10.1104/pp.63.3.531

Proline Oxidase and Water Stress-induced Proline Accumulation in Spinach Leaves 1

Anthony H C Huang a,2, Anthony J Cavalieri a
PMCID: PMC542864  PMID: 16660761

Abstract

Spinach (Spinacia oleracea L.) leaf discs accumulated free proline when exposed to polyethylene glycol solutions of water potential less than −10 bars. At −20 bars, the accumulation was 11 micromoles per gram original fresh weight in a 24-hour period.

When the leaf organelles were separated on a sucrose gradient, a proline oxidase was detected in the mitochondrial fraction. Isolated mitochondria were used for the study of the properties of the enzyme which was assayed by both oxygen uptake measurement and reduction of 2,6-dichlorophenol-indophenol in the presence of phenazine methosulfate. There was a stoichiometry of one-half mole of oxygen uptake per mole of Δ1-pyrroline-5-carboxylate production in the enzymic reaction. The enzyme had an optimal activity at pH 8.0 to 8.5 and an apparent Km value of 0.028 molar for proline. MgCl2 and flavin adenine dinucleotide were required for maximal activity. Addition of sucrose, mannitol, or polyethylene glycol to reduce the water potential of the reaction mixture to as low as −20 bars resulted in little inhibition. The enzyme preparation was unable to reduce NAD to NADH, and NAD did not inhibit the enzyme activity. The enzyme preparation reduced cytochrome c in the presence of KCN. Triton X-100 at low concentration strongly inhibited the enzyme activity. The enzyme was apparently linked to the mitochondrial electron transport system. The in vitro activity of the enzyme under optimal assay conditions was high enough to prevent proline accumulation under water stress condition; presumably this activity was restrained in vivo.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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