Soluble electron-transport activities in fresh and aged turnip tissue.

Area of Science:

• Plant Biochemistry
• Enzymology
• Cellular Metabolism

Background:

• Soluble turnip fractions exhibit reductase activity towards FeCN and DCPIP.
• Aging turnip tissue enhances these activities and develops NADH-cytochrome c reductase.

Purpose of the Study:

• To characterize the reductases present in turnip tissue.
• To investigate the origin and synthesis of these enzymatic activities.

Main Methods:

• Enzyme assays using NADH/NADPH, FeCN, DCPIP, and cytochrome c.
• Protein fractionation using (NH4)2SO4 precipitation and Sephadex chromatography.
• pH optima determination and inhibitor studies (6-methylpurine, ethionine, cycloheximide).

Main Results:

• At least three distinct reductases were identified: NADH-cytochrome c reductase, NADH-FeCN reductase, and NAD(P)H-DCPIP/FeCN reductase.
• Acid pH optimum for the vacuolar NAD(P)H-DCPIP/FeCN reductase; neutral optima for cytoplasmic NADH-cytochrome c and FeCN reductases.
• NADH-FeCN reductase may be a soluble form of microsomal NADH dehydrogenase; NADH-cytochrome c reductase is likely soluble and involved in cyanide-sensitive oxidation.
• Enzyme synthesis depends on RNA and protein synthesis, with cycloheximide inhibition reversible after prolonged washing.

Conclusions:

• Turnip tissue contains multiple soluble reductases with distinct subcellular origins and substrate specificities.
• The development of these reductase activities is regulated at the level of gene expression and protein synthesis.
• These findings provide insights into plant metabolic pathways and enzyme regulation.