Membrane-Bound Enzymes from Mycobacterium phlei; Malate Vitamin K Reductase
It is widely recognized that the enzymes of the living cell operate within the framework of a highly organized structure or by intracellular compartmentalization. A large number of cellular enzymes are located in membranes and referred to as membrane-bound enzymes. Included in this category are the enzymes located in the plasma membrane, mitochondria, and microsomes, as well as those found in bacteria and plant membranes. In fact, this definition can be extended to those proteins which catalyze the physical translocation of substrates and are responsible for transmembrane transport of solutes against a concentration gradient. The existence of membrane-bound enzymes has been known for many years, but not much attention has been given to them for detailed studies since either their structural organization or functions are lost on isolation. However, in the last 10 years, it has become clear that many membrane-bound enzymes require the lipid components of membranes for activity and that the previous difficulties in solubilization of these membrane components were due to the failure to recognize the lipid requirements. Nevertheless, it should be emphasized that enzyme complexes which require physical and spatial orientation to one another must remain intact for enzymatic activity.
KeywordsOxidative Phosphorylation Reductase Activity Membrane Vesicle Malate Dehydrogenase Nonheme Iron
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