Stable Suppression of Lactate Dehydrogenase Activity during Anoxia in the Foot Muscle of Littorina littorea and the Potential Role of Acetylation as a Novel Posttranslational Regulatory Mechanism

Table 2

Kinetic and structural analysis of partially purified control and 24 h anoxic foot muscle LDH.

	Control	24 h anoxic
Pyruvate 𝐾𝑚 (mM)	0.29±0.01	0.27±0.01
Lactate 𝐾𝑚 (mM)	25±2	23.6±0.8
𝑉max (pyruvate-reducing direction; U/g wet weight)	64±1	38±1^∗
ATP 𝐼50 (mM)	13±1	28±3^∗
ADP 𝐼50 (mM)	23±2	100±6^∗
Succinate	N.E.	N.E.
Aspartate	N.E.	N.E.
𝐸𝑎 (at pH 6.5; Kcal/mol)	62.4±0.5	72±1^∗
𝐸𝑎 (at pH 7.4; Kcal/mol)	58±3	64±3

The data are means ± SEM, 𝑛≥3 independent determinations on individually prepared samples. *indicates a significantly different result as compared to the control value using Student’s 𝑡-test, 𝑃<0.05. Note that the activation energy (𝐸_𝑎) values for control and 24 h anoxic LDH were assessed on fully pure enzyme samples.