Abstract
The intramitochondrial localization of the urea cycle enzymes, carbamoyl phosphate synthetase and ornithine transcarbamoylase, has been examined by both in vitro and in situ studies. The following three lines of evidence are presented to establish that significant fractions of the rat liver enzymes are loosely associated with the inner mitochondrial membrane: 1) when the mitochondrion is fractionated, the enzymes partition between the matrix and membrane fractions in the absence of detergent and partition solely to the matrix in the presence of detergent; 2) the purified enzymes associate with purified inner membrane preparations; and, 3) protein A-gold electron microscopic immunocytochemical analysis of rat liver sections reveals a nonrandom arrangement of the enzyme, with the maximal enzyme density adjacent to the inner mitochondrial membrane. These findings serve as the basis for novel potential mechanisms for regulation of the activity of the enzymes and provide additional evidence for the extensive organization of the mitochondrial matrix. The membrane interaction might also serve as the organizing factor for a carbamoyl phosphate synthetase-ornithine transcarbamoylase or other multienzyme complex.
Highlights
The intramitochondrial localization of the urea cycle the enzymes partition between the matrixand membrane enzymes, carbamoyl phosphate synthetase and orni- fractions in the absence of detergent and partition solely to thine transcarbamoylase, has been examined by both the matrix in the presence of detergent; 2) the purified enin vitroand in situstudies
These findings serve as the basis for novel potential mechanisms for regulation of the activity of the enzymes and provide additional evidence for the extensive organization of the mitochondrial matrix
Release of Membrane-associatedMitochondrialProteins with Increasing Concentrationsof Triton X-100-The association of carbamoyl phosphate synthetase with the inner mitochondrial membrane was suggested by the observation, by Clarke and Farber [22] and by our lab,' that the enzyme partitioned between matrixandinner membrane fractions that were prepared by digitonin treatment, by osmotic shock, or by freeze-thawing
Summary
The intramitochondrial localization of the urea cycle the enzymes partition between the matrixand membrane enzymes, carbamoyl phosphate synthetase and orni- fractions in the absence of detergent and partition solely to thine transcarbamoylase, has been examined by both the matrix in the presence of detergent; 2) the purified enin vitroand in situstudies. In the presence of detergent; 2) the purified enzymes associate with purified inner membrane preparations; and, 3) protein A-gold electron microscopic immunocytochemical analysis of rat liver sections reveals a Materials-Rat liver carbamoyl phosphate synthetase I
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