Malic enzyme from the rat mammary gland

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Malic enzyme (EC 1.1.1.40) plays a crucial role in metabolic pathways.
• Understanding the regulation of malic enzyme is important, particularly in tissues like the mammary gland during lactation.

Purpose of the Study:

• To purify and characterize malic enzyme from rat mammary tissue and liver.
• To compare the properties of malic enzyme from these two distinct tissues.
• To investigate the mechanism regulating malic enzyme activity during the lactation cycle.

Main Methods:

• Purification using ammonium sulphate precipitation, affinity chromatography, and ion exchange chromatography.
• Biochemical characterization including molecular weight and kinetic analysis.
• Immunochemical analysis using antibodies and single radial immunodiffusion assays.

Main Results:

• Malic enzyme from rat mammary tissue and liver exhibited similar subunit and native molecular weights, as well as comparable kinetics for malate and NADP+.
• Antibodies generated against the enzyme from one tissue cross-reacted with the enzyme from the other tissue, indicating immunochemical similarity.
• Single radial immunodiffusion assays demonstrated an immunochemical identity between the mammary and liver enzymes.
• The significant changes in malic enzyme activity observed during lactation were attributed to variations in the total amount of enzyme protein, not to post-translational activation.

Conclusions:

• Rat mammary and liver malic enzymes are immunochemically identical.
• The regulation of malic enzyme activity during lactation is primarily controlled by the amount of enzyme protein present.