Ketoglutarate dehydrogenase from ribbed mussel gill mitochondria: Modulation by adenine nucleotides and calcium ions
✍ Scribed by Karam, George A. ;Paynter, Kennedy T. ;Bishop, Stephen H.
- Publisher
- John Wiley and Sons
- Year
- 1987
- Tongue
- English
- Weight
- 800 KB
- Volume
- 243
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
The transient accumulation of proline in the gills of the osmotically stressed ribbed mussel (Modwlus demissus), may be controlled by a transient regulation of the a-ketoglutarate dehydrogenase (KGDH) activity. In this study, KGDH was partially purified from lysed mitochondria of gill tissue by differential centrifugation techniques. Various modulators of enzyme activity assayed at a saturating concentration (2.5 mM) of ketoglutarate (KG), showed inhibition by high concentrations of C1-(10-100 mM) and a slight activation or inhibition by the other compounds (10 mM), when assayed in the absence of added Ca++. Addition of C a + + at pH 7.2 caused no change in KSo.5 for KG and a 1.5-fold increase in V, , whereas at pH 7.8, no change in V,, but a 40-50% decrease in Ks0.5 and slight positive cooperative effects (%,pp" 1.4-1.7) were observed. At pH 7.8, addition of adenine nucleotides (AMP, ADP, ATP at 5mM) had no effect on the Vmax; however, ATP and ADP lowered the Ks0.5 by 3.54-fold. The CoA derivatives of short chain fatty acids were found to inhibit the enzyme by 30-60%. This inhibition was reversed by C a t + but only at higher KG concentrations (250 pM). The enzyme showed a major change in activity at nicotinamide adenine dinucleotidelreduced nicotinamide adenine dinucleotide ratio (NAD/NADH) < 1, an effect that could not be modified by Ca' + . It appears, therefore, that the mussel gill KGDH is mainly regulated by changes in mitochondrial pH and ketoglutarate or adenine nucleotide levels, rather than by changes in mitochondrial calcium levels.