Abstract
Best and McHenry 1 reported observations on a histamine-inactivating substance or system which they denote as histaminase. They state that oxygen is consumed during this reaction but have postponed a detailed manometric study until obtaining a more concentrated histaminase preparation. We have found that a kidney powder, prepared according to their directions, when added to histamine gave sufficient gas changes to study the histamine-histaminase reaction from the standpoint of oxygen uptake.
The experiments were performed in the Bar croft-Warburg apparatus, with air in the gas space, phosphate buffer in the conical vessel, KOH in the well, and a measured amount of histamine in the side bulb. Since attempts at materially purifying the enzyme were unsuccessful, 200 mg. dry kidney powder from the dog were used in the phosphate solution as a source of histaminase. When the system was at a constant temperature, 37.5°C, the histamine was tipped into the vessel and manometric readings were made at regular intervals until the oxidation ran to completion. Parallel experiments were always made without histamine because the powder alone had a small oxygen uptake. (Ca 25% of that with histamine.) This was subtracted in every case from the values found with the addition of the base.
The rate of oxidation early in the experiments was constant. Ten minute observations of the histamine oxidation plus the gas change due to kidney powder averaged about 6 to 8 cmm. of oxygen. When the oxygen uptake had ceased, the histamine was inactivated as shown by its failure to contract guinea pig intestine in vitro. On the other hand, when the oxygen uptake was not complete, the substrate was capable of contracting smooth muscle. This was observed in several experiments.
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