Quantitative dehydrogenase histochemistry with exogenous electron carriers (PMS, MPMS, MB)

Area of Science:

• Biochemistry
• Histochemistry
• Enzymology

Background:

• Electron carriers are crucial for biochemical and histochemical assays involving dehydrogenases.
• Phenazine methosulfate (PMS), 1-methoxy-phenazine methosulfate (MPMS), and Meldola Blue (MB) are commonly used electron carriers.
• Understanding their relative efficiencies under various conditions is essential for accurate enzyme activity determination.

Purpose of the Study:

• To compare the relative efficiencies of PMS, MPMS, and MB as electron carriers.
• To evaluate these carriers in both biochemical (non-enzymic) and quantitative histochemical assays.
• To determine the influence of different reaction media and pH on carrier performance.

Main Methods:

• Biochemical assays using a non-enzymic NADH-tetrazolium salt test.
• Quantitative histochemistry on heart and kidney slices.
• Assays focused on succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH) activities.
• Varied reaction media including aqueous, agarose, and polyvinyl alcohol (PVA).

Main Results:

• MPMS exhibited the highest electron transfer velocity in biochemical assays, independent of pH (7.0-8.5).
• PMS and MB showed lower transfer abilities biochemically, with varying efficiency depending on the tetrazolium salt (iodonitrotetrazolium chloride vs. nitro blue tetrazolium chloride).
• Histochemical results differed significantly from biochemical findings, with MPMS showing higher LDH activity and PMS/MB showing comparable SDH activity in agarose media, but PMS superior in aqueous media.

Conclusions:

• The efficiency of electron carriers like PMS, MPMS, and MB is highly dependent on the specific histochemical incubation conditions, tissue type, preparation, and the target dehydrogenase.
• Generalizations about electron carrier efficiency based on single experimental setups are not scientifically justified.
• Careful selection and optimization of electron carriers are necessary for reliable histochemical enzyme activity measurements.