Background: A high level of replication is one of the main indicators of tumors.
Tumor cells have to manufacture and transport macromolecules into daughter cells. One
of the required enzymes is malic enzyme, which generates the NADPH for fatty acid
synthesis in order to make cell membrane and pyruvate, and support the glycolysis
pathway to supply the energy demand. Due to the enormous proliferation of cancer cells,
it is likely that the activity of malic enzyme in cancer cells is more than normal cells.
The aim of this study is to survey the kinetics of malic enzyme in tumor and normal
breast tissues.
Methods: We obtained the tumor and normal breast tissue specimens directly
from the operating room. The assays were performed with partially purified samples
under optimum conditions for the substrate and co-factor requirements. The velocity
of the enzyme or Michaelis-Menten constant, maximum velocity, and the amount of
inhibitor that reduced the enzyme activity by 50% were obtained and calculated in all
samples.
Results: The Michaelis-Menten constant for malate was lower in tumors compared
to normal samples. In contrast, the maximum velocity for malate in tumors was higher
than normal tissues, whereas the amount of inhibitor that reduced the enzyme activity
by 50% of guanidine hydrochloride and sodium chloride were both higher in tumors
than normal tissues.
Conclusion: The obtained results indicated that the malic enzyme kinetics had
different patterns in tumor tissues in comparison with normal tissues. A higher affinity
of malic enzyme for pyruvate production in tumors supported high aerobic glycolysis.
Moreover, it could be an approach to connect glutaminolysis to the glycolysis pathway.
Malic enzyme could be a target to inhibit the glycolysis and glutaminolysis pathways
in tumors.