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Kinetic studies of nitrogenase from soya-bean root-nodule bacteroids.

ABSTRACT: The apparent Michaelis constants [K'(N(2)) and K'(C(2)H(2))] and the corresponding apparent maximum velocity values (V') for soya-bean bacteroid nitrogenase increased concomitantly in response to increases in nitrogenase Fe-protein concentration and ATP concentration in cell-free assays and in response to O(2) pressure in intact nodules and bacteroid suspensions. K'(C(2)H(2)) in cell-free assays was also affected by pH and by Na(2)S(2)O(4) concentration. Nitrogenase Fe-protein behaved as a catalytic effector reacting at interacting sites on the nitrogenase Fe-Mo-protein. The results indicated that the Fe-Mo-protein probably bears the catalytic sites for N(2) and C(2)H(2) reduction. It is concluded that reduction of N(2) or C(2)H(2) by this nitrogenase involves a reaction mechanism with a sequence of unknown order. The sequence in which substrate, enzyme, effector, ATP and reductant react determines which of the various rate-constants are involved in the apparent Michaelis constant, whose true kinetic meaning was thus unresolved.

SUBMITTER: Bergersen FJ

PROVIDER: S-EPMC1177439 | biostudies-other | 1973 Jan

REPOSITORIES: biostudies-other

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Project description:The aim of this experiment was to explore transcriptomic changes in the distal gut of Altantic salmon fed five experimental and two control diets. The experimental diets were isonitrogenous, isolipidic and isocaloric. They had similar content of fish meal (~22%) and similar total plant protein content (~45%), but differed in the contents of soya protein concentrate (SPC) and bean protein concentrate (BPC). These two ingredients were used to replace each other (either partially or fully) at the levels of incorporation ranging from 0 to 45%, with ~11% increments. As a result, the experimental diets contained either 45% SPC and 0% BPC (S45), 34% SPC and 11% BPC (S34B11), 22% SPC and 22% BPC (S22B22), 11% SPC and 34% BPC (S11B34) or 0% SPC and 45% BPC (B45). The S45 and B45 diets were single plant protein diets, while the others (S34B11, S22B22 and S11B34) were mixed plant protein diets. The control diets were enriched with fish meal (FM diet) or soybean meal (SBM diet) to provide negative and positive controls for gut inflammation (enteritis), respectively. The study was conducted at EWOS Innovation Research Facility in Dirdal (Norway) Atlantic salmon (Salmo salar L.) of the SalmoBreed strain were supplied as fertilized eggs and hatched on site. Mixed-sex juvenile salmon in groups of ~150 fish were transferred to 26 indoor tanks (0.6 x 0.6 x 0.6 m), with ~60 L of freshwater flowing at a rate of 3.9 L/min and continuous aeration. The temperature of water was regulated at 13°C and all animals were exposed to a constant light regime (24 h light/day). Fish were fed a commercial EWOS Start 1 diet and acclimated to the experimental conditions for 2 weeks, after which (at body mass ~1.5 g) they were subjected to a 56-day feeding trial. Tanks were randomly assigned to the dietary treatments, with 4 replicate tanks per each experimental diet (S45, S34B11, S22B22, S11B34 and B45) and 3 replicate tanks per each control diet (FM and SBM diets). Fish were fed to satiation prior to the feeding trial and during the dietary manipulation using automatic band feeders (Holland Technology, Norway). During the feeding trial, all fish in each tank had their biomass recorded on days 0 (start of experiment), 14, 28, 42 and 56 (end of experiment) for evaluation of growth performance.

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Kinetic studies of nitrogenase from soya-bean root-nodule bacteroids.

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