EurekaMag.com logo
+ Site Statistics
References:
47,893,527
Abstracts:
28,296,643
+ Search Articles
+ Subscribe to Site Feeds
EurekaMag Most Shared ContentMost Shared
EurekaMag PDF Full Text ContentPDF Full Text
+ PDF Full Text
Request PDF Full TextRequest PDF Full Text
+ Follow Us
Follow on FacebookFollow on Facebook
Follow on TwitterFollow on Twitter
Follow on Google+Follow on Google+
Follow on LinkedInFollow on LinkedIn

+ Translate

Ph regulation of mitochondrial branched chain alpha keto acid transport and oxidation in rat heart mitochondria






Journal of Biological Chemistry 262(20): 9629-9635

Ph regulation of mitochondrial branched chain alpha keto acid transport and oxidation in rat heart mitochondria

The kinetics of branched chain .alpha.-keto acid uptake and efflux were studied as a function of varied external and matrix pH. Matrix pH was determined by the distribution of 5,5'-dimethyloxazolidine-2,4-dione. When rat heart mitochondria were incubated under transport conditions at pH 7.0 with succinate as respiratory substrate, the matrix pH was significantly > 8.0. Matrix pH remained .gtoreq. 8.0 when the medium pH was varied from 6.3 to 8.3, and it was lowered below 8.0 by addition of 5 mM phosphate or uncoupler. No pH gradient was detectable when mitochondria were incubated in the presence of valinomycin and uncoupler. Efflux of .alpha.-ketoisocaproate or .alpha.-ketoisovalerate from rat heart mitochondria obeyed first order kinetics. Varying the external pH from 6.6 to 8.3 had no significant effect on efflux, and at an external pH of 7.0, the first order rate constant for efflux was not affected by decreasing the matrix pH. On the other hand, exchange was sensitive to changes in medium but not matrix pH. The K0.5 for external branched chain .alpha.-keto acid was lowered by changing the medium pH from 7.6 to 6.3. At medium pH values .gtoreq. 8.0 both K0.5 and Vmax were affected. Uptake was determined either by measuring initial rates or was calculated after measuring the first order approach to a final equilibrium value. Unlike efflux, uptake was sensitive to changes in both external and matrix pH. The rate of branched chain .alpha.-keto acid uptake was stimulated by decreasing the medium pH from 8.3 to 6.3 and by alkalinization of the mitochondrial matrix. The estimated external pK for proton binding was 6.9. The data inidcate that the branched chain .alpha.-keto acid transporter is asymmetric, that is, binding sites for substrate on the inside and outside of the mitochondrial membrane are not identical. .alpha.-Ketoisocaproate oxidation was measured at 37.degree. C in isolated mitochondria over the pH range of 6.6 to 8.1. Changes in the rate of branched chain .alpha.-keto acid oxidation, particularly when ATP was added (.uparw. .DELTA.pH), were found to parallel the pH effects observed on branched chain .alpha.-keto acid uptake. Therefore, transport, and by implication oxidation, can be regulated by pH changes within the physiological range. Furthermore, intracellular pH may affect the degree of compartmentation between the cytosolic and mitochondrial branched chain .alpha.-keto acid pools.


Accession: 006092007

PMID: 3597428



Related references

Hutson, Susan M., 1987: PH regulation of mitochondrial branched chain a-keto acid transport and oxidation in rat heart mitochondria. The Journal of Biological Chemistry 262: 29-35

Hutson, S.M., 1987: pH regulation of mitochondrial branch chain alpha-keto acid transport and oxidation in rat heart mitochondria. The kinetics of branched chain alpha-keto acid uptake and efflux were studied as a function of varied external and matrix pH. Matrix pH was determined by the distribution of 5,5'-dimethyloxazolidine-2,4-dione. When rat heart mitochondria were...

Hutson S.M.; Wallin R.; Roten S., 1991: Partial purification of branched chain alpha keto acid bcka and pyruvate transport activities from rat heart mitochondria. FASEB Journal 5(6): A1755

Hutson, S.M.; Hall, T.R., 1993: Identification of the mitochondrial branched chain aminotransferase as a branched chain alpha-keto acid transport protein. Conditions were developed which optimized reconstitution of branched chain alpha-keto acid transport activity, which was measured as alpha-ketoisocaproate (KIC) transport, and pyruvate transport activity. Reconstitutable KIC transport activity was...

Kochi H.; Seino H.; Ono K., 1986: Inhibition of glycine oxidation by pyruvate alpha ketoglutarate and branched chain alpha keto acids in rat liver mitochondria presence of interaction between the glycine cleavage system and alpha keto acid dehydrogenase complexes. Pyruvate, .alpha.-ketoglutarate, and branched-chain .alpha.-keto acids which were transaminated products of valine, leucine, and isoleucine inhibited glycine decarboxylation by rat liver mitochondria. However, glycine synthesis (the reverse reacti...

Kochi, H.; Seino, H.; Ono, K., 1986: Inhibition of glycine oxidation by pyruvate, alpha-ketoglutarate, and branched-chain alpha-keto acids in rat liver mitochondria: presence of interaction between the glycine cleavage system and alpha-keto acid dehydrogenase complexes. Pyruvate, alpha-ketoglutarate, and branched-chain alpha-keto acids which were transaminated products of valine, leucine, and isoleucine inhibited glycine decarboxylation by rat liver mitochondria. However, glycine synthesis (the reverse reaction o...

Harris R.A.; Han A.C.; Goodwin G.W.; Kuntz M.J.; Paxton R., 1986: Regulation of the activity state of rat liver branched chain alpha keto acid dehydrogenase by branched chain alpha keto acids. Federation Proceedings 45(3): 233

Drown, P.M.; Torres, N.; Tovar, A.R.; Davoodi, J.; Hutson, S.M., 2000: Use of sulfhydryl reagents to investigate branched chain alpha-keto acid transport in mitochondria. The goal of this paper was to determine the contribution of the mitochondrial branched chain aminotransferase (BCATm) to branched chain alpha-keto acid transport within rat heart mitochondria. Isolated heart mitochondria were treated with sulfhydr...

Hutson S.M., 1986: Influence of ph on the branched chain alpha keto acid transporter in rat heart mitochondria. Federation Proceedings 45(6): 1757

Espinal, J.; Beggs, M.; Randle, P.J., 1988: Assay of branched-chain alpha-keto acid dehydrogenase kinase in mitochondrial extracts and purified branched-chain alpha-keto acid dehydrogenase complexes. Methods in Enzymology 166: 166-175