| Research Abstract |
Methionine sulfoxide (MSO) is recognized to be available as a methionine source for mammals. The present study was designed to demonstrate a hypothesis that ruminant animals might have higher MSO reductase activity than did monogastric animals.
At first, optimal conditions for assaying the enzyme activities were examined using the livers and kidneys of both catle and swine slaughtered in a meat plant in Miyazaki city. Since the enzyme activity was found chiefly in homogenate and supernatant fluid after centrifugation in bth tissues of both animals, the supernatant fluid was used hereafter for assaying the activity. Optimum PH and temperature examined were as follows: cattle liver: PH 6.0, 33 C; cattle kidney: PH 6.7, 39 C; swine liver and kidney: PH 7.0, 37 c. The effects of reducing agents on the activity examined were shown to be that both in cattle and swine, NADH and NADPH equally stimulated the activity in liver, while only NADPH did in kidney. The substrate concentrations (mM) for obtaining the maximum velocity (activity) and Km (mM) examined under the optimum conditions using NADH for liver and NADPH for kidney as reducing agents were as follows: cattle liver: 0.80, 0.158; cattle kidney: 0.60, 0.064; swine liver: 0.25, 0.049; swine kidney: 1.00, 0.116.
Finally, under the conditions to gain the maximum activity (but temperature was fixed at 39 c), 17 heads of cattle and 12 heads of swine were supplied for determining the average enzyme activities of both animals. As a result, though the activty of swine appeared to show relatively centralized values, the activity in cattle varied from animal to animal. This point led us to presume that MSO reductase might be an inducible enzyme. Taking an average, the activity of cattle liver (expressed as nmol of methionine per unit weight of the tissue) was 3.6 times higher than that of swine liver, and cattle kidney was 1.15 times as high as swine kidney.
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