TPNH oxidase enzymes

Ascorbic Acid-dependent DPNH-Oxidase Microsomes of adrenal medullas contain an enzyme which oxidizes DPNH but not TPNH, and like the similar enzyme from plant tissues (K2, N2) utilizes oxidized ascorbic acid but not dehydroascorbic acid as the acceptor. Complexed Fe + in ferricyanide or cytochrome c can also serve... 

Tn the past few years considerable information has accumulated regard-ing hydroxylating enzymes which form a subgroup of the class termed mixed-function oxidases by Mason (15) or monooxygenases by Hayaishi (13). The reactions catalyzed by these enzymes are characterized by their dependence on TPNH and molecular oxygen of which one atom is incorporated into a lipid-soluble specific substrate. For the most part these oxidases are localized in the endoplasmic reticulum (the microsome... 

The demonstration by Phillips and Laiigdon (1956) that the level of TPNH-cytochromc c reductase is increased in the livers of hyperthyroid rats and reduced in those of hypothyroid animals is of particular interest. Since the activity of this enzyme results in the production of triphospho-pyridiiie nucleotide (TPN), a cofactor required for many oxidative enzymes, this change is probably a direct reflection of the general over-all acceleration of oxidative processes, and, more specifically, of those which are TPN-linked. Decreased activity of lactic dehydrogenase (Vcstling and Knocpfelmacher, 1950) is compatible with the demonstrated ability of thyroxine to inhibit this enzyme in vitro (Wolff and Wolff, 1957 Radsma et al., 1957). Decreases in the in vivo activity of such enzymes as tyrosine oxidase, DOPA-decarboxylase, betaine-homocysteine transmethylase, and... 

The properties of mixed function oxidases are summarized in Table XVII. These enzyme systems oxidize both aromatic and aliphatic substances with consumption of oxygen. TPNH, DPNH, dihydroxy-fumarate, and o-diphenols serve as electron donors for reduction of one atom of the oxygen molecule. In general, metal-binding reagents inhibit enzymes of this class iron, copper, and possibly manganese form prosthetic groups. 

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