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Mitochondrial malic enzymes. An association between NAD(P)+-dependent malic enzyme and cell renewal in Sprague-Dawley
Abstract:
The activities of the mitochondrial NAD(P)+- and NADP+-dependent malic enzymes were measured in 11 tissues of the male Sprague-Dawley rat. The NAD(P)+-dependent malic enzyme was present in small intestinal mucosa, spleen, thymus, lung, and testis. Each of these tissues contain cells that are undergoing active rates of renewal. The NADP+-dependent malic enzyme was not confined to tissues undergoing cell renewal, and was present in mitochondria from brain, skeletal, and heart muscle, kidney, and lung and testis. Both enzymes were absent or at a low activity in normal and regenerating liver. The results support, and extent to nonneoplastic tissues, our proposal that cells which show active and sustained rates of renewal contain the NAD(P)+-dependent malic enzyme and have a unique intramitochondrial pathway for malate oxidation (Sauer, L.A., Dauchy, R.T., Nagel, W.O., and Morris, H.P. (1980) J. Biol. Chem. 255, 3844-3848).
Insights
Mitochondrial malic enzymes were studied in rat tissues. The NAD(P)+-dependent malic enzyme is found in rapidly renewing cells, supporting a unique malate oxidation pathway in these tissues.
Area of Science:
- Biochemistry
- Cell Biology
- Physiology
Background:
- Mitochondrial malic enzymes play roles in cellular metabolism.
- The distribution and function of these enzymes across different tissues are not fully understood.
- Previous research suggested a link between NAD(P)+-dependent malic enzyme and cell renewal.
Purpose of the Study:
- To investigate the activity and distribution of mitochondrial NAD(P)+-dependent and NADP+-dependent malic enzymes in various rat tissues.
- To determine if the presence of NAD(P)+-dependent malic enzyme correlates with tissues exhibiting high cell turnover rates.
- To extend previous findings on malate oxidation pathways to non-neoplastic tissues.
Main Methods:
- Enzyme activity assays were performed on mitochondrial extracts from 11 different tissues of male Sprague-Dawley rats.
- Specific measurement of NAD(P)+-dependent malic enzyme and NADP+-dependent malic enzyme activities.
- Comparison of enzyme activities across tissues with varying rates of cellular renewal.
Main Results:
- NAD(P)+-dependent malic enzyme was detected in small intestinal mucosa, spleen, thymus, lung, and testis, tissues characterized by active cell renewal.
- NADP+-dependent malic enzyme was found in a broader range of tissues, including brain, skeletal muscle, heart muscle, kidney, lung, and testis.
- Both enzymes showed low or absent activity in normal and regenerating liver tissue.
Conclusions:
- The findings support the hypothesis that cells with high and sustained renewal rates possess the NAD(P)+-dependent malic enzyme.
- These tissues appear to utilize a unique intramitochondrial pathway for malate oxidation.
- The distribution of NADP+-dependent malic enzyme suggests a role beyond just cell renewal, potentially in broader metabolic functions.