Cytochemical Demonstration and Metabolic Significance of Reduced Diphospho-Pyridinenucleotide and Triphospho-Pyridinenucleotide Reductases in Human Gingiva

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Abstract
Employing nitro blue tetrazolium (Nitro BT), human gingiva diphosphopy-ridine nucleotide reductase (DPNH2R) exhibited much higher overall activity than triphosphopyridine nucleotide reductase (TPNH2R). Purple and blue-purple formazan DPNH2R and TPNH2R reactions occurred in blood vessels, nerves and cells of the connective tissue. Positive formazan reactions also were observed in the cytoplasm of all epithelial cells except those of the parakeratin and keratin. The parakeratin exhibited endogenous reducing activity characterized by pink-violet to violet colors. Keratin remained unreactive in all sections. Cyanide always intensified formazan reaction (competition with Nitro BT for electrons by a terminal oxidizing system). DPNH2R, most active in the stratum basale, decreased progressively to and through the stratum granulosum. TPNH2R, most active in the stratum granulosum, decreased progressively to and through the stratum spinosum, becoming more reactive in the stratum basale. Desmosomes, tonofibrils, intercellular bridges and nucleoli of the epithelial cells exhibited positive purple formazan reactions for both enzymes, suggesting a broad metabolic role for these organelles. Many TPNH2R and lesser DPNH2R specific blue staining granules (probably kera-tohyalin) were observed in the stratum granulosum sparsely extending into the parakeratin. An oxidative metabolic pathway, whose reductive phase is primarily dependent upon TPN (Pentose Shunt) and secondarily upon DPN (Krebs Cycle), has been proposed for the formation of the keratin precursor substance, parakeratin, and keratin. Its terminal oxidizing system also was considered.