Uncoupling of mitochondrial respiration by ADP

Even when oxidative phosphorylation is blocked completely by addition of high concentrations of oligomycin plus aurovertin, the addition of ADP to a suspension of mitochondria containing a high concentration of ATP inside the mitochondria induces a stimulation of respiration and oxidation of nicotinamide nucleotide. It is concluded that transport of ADP into mitochondria with a high endogenous ATP/ADP ratio requires energy.

Nitrate poisoning in cattle. 2. Changes in nitrite in rumen fluid and methemoglobin formation in blood after high nitrate intake

2. Three experiments with mature dry Friesian cows lasted for up to 16 days. Nitrate was given as nitrate-rich hay or mixed with concentrates to supply from 2.4 to 16.0 g/100 kg liveweight at each meal. To test the hypothesis that methaemoglobin was formed as the result of the production of nitrite as an intermediate in the rumen, one group was given a daily supplement of KNO2, 2 to 3 g/100 kg liveweight. Blood was sampled at frequent intervals, and ruminal fluid was sampled every 15 min for short periods from cows with a recirculating sampling device. Large intakes of nitrate in either form increased nitrite in the rumen, leading to increase of methaemoglobin in the blood during the first few days, after which the high value was maintained. The high methaemoglobin value was positively correlated with the larger nitrite content in the rumen. Results are discussed in the light of conflicting reports on the tolerance of cattle to large amounts of nitrate and the importance of frequent sampling to obtain a true picture is stressed. Previous inferences regarding the ability of cattle to tolerate nitrate at up to 90 g/100 kg are considered to be mistaken. ADDITIONAL ABSTRACT: In two experiments groups of 4 cows (415-669 kg body weight) received similar daily amounts of NO3- as either a single oral dose of KNO3 (15 g/100 kg) or a single feed of nitrate rich hay (12.4-15.4 g NO3-/100 kg) for 18 days. In a third experiment 6 cows received 2 or 3 g/100 kg of NO3- as a single oral dose of KNO2 for 6 days. Nitrate, nitrite and ammonia were measured in rumen sample and haemoglobin and methaemoglobin were measured in blood. The daily supply of equal doses of nitrate to cows, as hay with a high nitrate content or as potassium nitrate, induced higher nitrite contents in the rumen fluid and a higher percentage of methaemoglobin in the blood during the first days, after which they remained on this higher level. These increases were probably due to a change in the activity of the reducing micro-organisms in the rumen. The changes also partly explain the controversial data in the literature on the acceptable dosages of nitrate to be supplied to ruminants. This may have led to the mis-interpretation that ruminants should tolerate daily intakes up to 90 g of NO3- per 100 g body weight. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Role of the intramitochondrial adenine nucleotides as intermediates in the uncoupler-induced hydrolysis of extramitochondrial ATP

1. A formula is given that describes the appearance of [14C]ATPADP outside the mitochondria after the addition of [14C] 1atp during the steady-state uncoupler-induced hydrolysis of extramitochondrial ATP. If the transported adenine nucleotides equilibrate with the intramitochondrial pool, [14C]ADP0 would be expected to appear with a lag phase that corresponds with the time needed for the radioactive labelling of the intramitochondrial adenine nucleotide pool. 2. The rates of formation of [14C]ADP outside the mitochondria after addition of [14C]ATP during the steady-state uncoupler-induced ATP hydrolysis catalysed by rat-liver mitochondria at 0 degree C were measured. 3. In the presence of carbonyl cyanide m-chlorophenylhydrazone the time course of the [14]ADPo formation was the same as that predicted on the basis of the above assumption. 4. In the presence of the less effective uncoupler, 2,4-dinitrophenol, the time course of [14C]ADPo formation was not consistent with the theoretical predictions: no lag phase was present and the measured rate was higher than the maximal calculated rate. These results can be explained by assuming a functional interaction between the adenine nucleotide translocator and the mitochondrial ATPase (F1). 5. It is concluded that under phosphorylating as well as dephosphorylating conditions, the adenine nucleotide translocator and the mitochondrial ATPase can be functionally linked to catalyse phosphorylation or dephosphorylation of extramitochondrial ADP or ATP, without participation of the intramitochondrial adenine nucleotides.

Nucleotide-binding properties of native and cold-treated mitochondrial ATPase

1. The bound nucleotides of the beef-heart mitochondrial ATPase (F1) are lost during cold inactivation followed by (NH4)2SO4 precipitation. The release of tightly bound ATP parallels the loss of ATPase activity during this process. 2. During cold inactivation, the sedimentation coefficient (s20, w) of the ATPase first declines from 12.1 S to 9 S, then to 3.5 S. (NH4)2SO4 precipitation of the 9-S component also leads to dissociation into subunits with s20, w of 3.5 S. 3. The 9-S component still contains the bound nucleotides, which are removed when it dissociated into smaller subunits. 4. Reactivation of cold-inactivated ATPase by incubation at 30 degrees C is increased by the presence of 25% glycerol. ATP, however, does not have any clearcut effect on the degree of reactivation in the presence of glycerol. 5. ADP is an inhibitor of the reactivation, probably because it exchanges during reactivation for bound ATP giving rise to an inactive 12-S component. 6. The exchange of tightly bound nucleotides with added adenine nucleotides is more extensive and faster with cold-inactivated ATPase than with the native enzyme. During reactivation up to 1.6 moles of ATP and 1.0 mole ADP can exchange per mole enzyme. 7. Incubation with GTP, CTP or inorganic pyrophosphate induces an increased activity of the ATPase, which, however, soon declines in the presence of ATP. It also disappears on precipitation of GTP-treated enzyme with (NH4)2SO4.

The possible role of tightly bound adenine nucleotides in oxidative and photosynthetic phosphorylation

The tightly bound nucleotides of the beff-heart mitochondrial ATPase are released during cold inactivation followed by ammonium sulfate precipitation. During incubation at 0 degrees C the sedimentation coefficient (S20W) of the ATPase first declines from 12.1S to 9S. Prolonged incubation or precipitation with ammonium sulfate leads to dissociation of the 9S component into subunits with S20W of 3.5S. The 9S component still bears bound nucleotides which exchange more extensively and rapidly with added nucleotides than those bound to the active 12.1S component. The bound nucleotides are lost when the 9S form dissociates into the smaller subunits. Thus, firm binding of nucleotides is a property of the quarternary structure of the enzyme. The exchangeability of the nucleotides bound to the ATPase of chloroplast membranes is greatly increased in membranes illuminated in the presence of pyocyanine. Pi can exchange into both the beta and gamma positions of the bound nucleotides when the membranes are energized in the presence of Mg2+. The exchange of the nucleotides and the incorporation of Pi are insensitive to the inhibitor Dio-9 but are inhibited by the uncoupler S13. This inhibition by S13 parallels that of the inhibition of photosynthetic phosphorylation. These findings are discussed with regard to our hypothesis that electron transfer causes release of preformed tightly bound ATP from the ATPase by inducing a conformational change.

Studies on the amount and composition of digesta flowing through the duodenum of dairy cows. 2. Sites of net absorption of magnesium and calcium from the alimentary tract

Two cows were fitted with re-entrant duodenal cannulas, and four with T-piece duodenal annulas. Balance trials were carried out, the cows receiving either a winter ration, or freshly-mown herbage. Direct measurements were made of the flow of digesta, and of the amounts of Mg and Ca in both duodenal and faecal samples. Also indirect measurements were made of these parameters, using polyethylene glycol and chromium sesquioxide indicators. Net Ca absorption was restricted to the intestines, and, at high Mg intake, net Mg absorption was also largely intestinal, though too large an error attached to the indirect measurement of Mg absorption rates for reliable conclusions to be drawn. There was considerable secretion of Ca proximal to the duodenum. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Cell-mediated immune responses in chronic liver diseases

Studies of the cell-mediated response to liver antigens, using the leucocyte migration test, in 163 patients with various liver disorders showed that abnormal responses were almost confined to active chronic hepatitis (53% abnormal), primary biliary cirrhosis (64%), and cryptogenic cirrhosis (29%). The test was also abnormal in five out of seven patients with jaundice due to drug hypersensitivity and in one patient with acute infectious hepatitis at a time when mitochondrial antibodies were present in the serum. More of those with active chronic hepatitis on prednisone or azathioprine had normal tests than of those who were untreated, and in 8 out of 10 examined serially during therapy there was an accompanying improvement in leucocyte migration. Abnormal responses to salivary gland or kidney antigens were also found in nearly half of those with features of Sjögren's syndrome or renal tubular acidosis as part of a multisystem involvement-this, though occurring in cryptogenic cirrhosis, was found with greater frequency in active chronic hepatitis and primary biliary cirrhosis. These cell-mediated immune responses, perhaps triggered by the initial damage to the liver from viral or other agents, may be responsible both for the perpetuation of the liver disease and, because of common surface antigens, for the damage to other organs.

Influence of higher fatty acids on the availability of magnesium in milking cows

The availability of dietary Mg for five lactating cows decreased in proportion to the amount of animal fat added to their winter ration. Previous workers have reported that increasing crude protein content of the herbage is associated with decreasing availability of Mg for the cow, and that the content of higher fatty acids in grass and hay increases with increasing crude protein content. It was suggested that nitrogen fertilizers increase the fat content of the herbage, thereby reducing the availability of Mg. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Sodium requirement of milking cows: balance trials with cows on rations of freshly mown herbage and on winter rations

Dairy cows were fed freshly mown herbage or winter rations which together with the drinking water gave Na intakes of betwen 5.8 and 91.0 g./day. The availability of the Na varied from 77 to 95% averaging 85.5%. The Na secretion in the milk averaged 0.38 g./l. varying from 0.31 to 0.49 g./l. The Na requirement for dairy cows with milk yields of 10-30 kg, /day when the Na was 75-95% available ranged from 10.0 to 23.3 g./day. D.E.C. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Hypomagnesaemia in milking cows: intake and utilization of magnesium from herbage by lactating cows

During 1958-60, 11 Mg balance trials were carried out with 39 lactating Friesian cows, which were fed indoors on a winter ration in 1 trial or on herbage freshly cut from pastures with different fertilizer treatments in the other trials. Average daily Mg intake was 33.08 g. for the winter ration and 16.62 g. for herbage, 17% of which was 'available', i.e. absorbed. Average Mg excretion in urine was 1.77 g., Mg excretion in milk 1.77 g./cow with an average content of 0.12 g./kg. milk, and Mg retention -0.5 g. Hypomagnesaemia occurred only when Mg excreted in urine was

Hypomagnesaemia in milking cows: the response of serum magnesium to alterations in herbage composition resulting from potash and nitrogen dressing on pasture

Detailed results presented in this paper were obtained during an experiment reported previously (D.S.A. 21 [872]) and concern relationships between fertilizer treatment of pasture, chemical composition of the herbage and serum Mg levels. A heavy potash dressing caused increases in herbage K and decreases of 15-20% in the Mg level, while a heavy N application increased crude protein and Mg levels in the herbage. There was a significant correlation between serum Mg levels and Mg contents of the herbage in the week preceding blood sampling; in 822 cows no low serum Mg levels were found when the Mg content of the herbage was >0.20%. Negative correlations between serum Mg levels and crude protein or K content were significant. There was no relationship between daily milk yield and serum Mg levels. M.P.H. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Influence of fertilizer treatment of grassland on the incidence of hypomagnesaemia and hypomagnesaemia tetany (grass tetany) in milking cows

In grazing experiments with 16 milking cows during 1956 and 1957 heavy K dressings lowered Mg levels of the blood serum, particularly in spring and autumn. Heavy N dressings had similar but less marked effects. The greatest differences were between light and heavy NK dressings. The mean differences were 0.82 mg per 100 ml serum over the whole growing season and >1.20 mg in spring and autumn. Heavy P dressings in autumn were accompanied by a slight drop in serum Mg. In 1957 grass tetany occurred in 6 cows on the heavy-K plots; the Mg level of these animals was 0.2-0.7 mg/100 ml serum. In an experiment on 23 farms the serum-Mg level of 90 milking cows decreased when they were released on pastures occupied the previous day by cows showing tetany; 60 % of them had an Mg level of

Grass tetany in grazing milking cows

Statistical investigation showed that correlation existed between the incidence of grass tetany and the mean 24-hr, temperature, particulary in spring and autumn. There was also a significant positive correlation between the K/(Ca and Mg) ratio in the grass and the incidence of tetany. During the spring and autumn, when the average temperatures were below 14 degrees C., an increase in K uptake by the herbage being grazed was associated with a rise in temperature, and was followed, after a 5-day time-lag, by an increase in the number of cases of tetany, if the critical value of K/(Ca + Mg) (2.2) was exceeded. A fall in temperature was followed by a fall in the ratio value and in tetany incidence. High summer temperatures were associated with a lower value for the ratio and only a few cases of tetany occurred. The results favour the theory that the relationship between temperature and the incidence of tetany is correlated with the cationic composition of the herbage grazed. [See Abs. 1013.]-From authors'summary. (Abstract retrieved from CAB Abstracts by CABI’s permission)