AJP - Heart and Circulatory Physiology, Vol 246, Issue 4 483-H490, Copyright © 1984 by American Physiological Society
Glutamic dehydrogenase activity in rat heart: demonstration of two forms of enzyme activity
H. G. McDaniel, M. Yeh, R. Jenkins, B. Freeman and J. Simmons
Glutamic dehydrogenase (GDH) activity in rat heart was found to be 2.1 U/g
of heart (wet wt). The mitochondrial glutamic dehydrogenase activity
accounted for only 18% of the total. This percentage of the total activity
in heart mitochondria was not altered by nagarse treatment, acetone
extraction, sonication in Triton X-100, and extraction with buffer
containing a protease inhibitor. The remainder of the activity was present
in the cytosol. Cytosolic GDH activity differed from mitochondrial GDH
activity by its pH curve, stability to heat, Arrhenius plot, and the effect
of different nucleotides. Acetone extraction of the mitochondria resulted
in GDH that was stable to heat and had a shallow temperature activation
curve resembling cytosolic GDH. Acetone extraction of cytosolic GDH
inactivated it. The cytosolic activity was purified 288-fold and the
mitochondrial activity 100-fold. Purified cytosolic and mitochondrial GDH
enzymes had different monomeric molecular weights on sucrose density
gradient centrifugation. Gel filtration of cytosolic and mitochondrial GDH
also showed different monomeric molecular weights. We conclude that rat
heart GDH exists in two forms with different physical and kinetic
characteristics. The majority of GDH activity in rat heart is cytosolic.
The mitochondrial enzyme has a lipid-soluble component that can be removed
with acetone without destroying its activity.
