Purification and properties of two malic enzyme activities in liver mitochondria of Squalus acanthias (spiny dogfish)

• Published in: Journal of Experimental Zoology
• Main Authors: Zhou, Xiaoqin, Korte, Joseph J., Anderson, Paul M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1995
• Subjects: Animal Science and Zoology; General Medicine; spiny dogfish; Squalus acanthias
• Online Access: http://dx.doi.org/10.1002/jez.1402720305; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjez.1402720305; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jez.1402720305

Abstract Two malic enzymes are present in liver mitochondria from Squalus acanthias (spiny dogfish), an NAD(P)‐dependent and an NADP‐dependent malic enzyme. The NAD(P)‐dependent enzyme was partially purified and found to have kinetic properties similar to other malic enzymes; the molecular weight is ≈ 130,000. The maximal rate with NADP is 40% of the maximal rate with NAD. The NADP‐dependent malic enzyme was purified to homogeneity and also has properties similar to other malic enzymes, including a subunit molecular weight of ≈ 61,000 and a native molecular weight of ≈ 250,000; however, the rate as a function of malate concentration is described by a sigmoid curve. Both enzymes require either Mn 2+ or Mg 2+ for activity, are activated by fumarate or succinate, and are inhibited by ATP. Both enzymes are inhibited by low concentrations of oxalacetate; the K i for competitive inhibition of the NAD(P)‐dependent malic enzyme by oxalacetate is 4 μM. The K m for Mn 2+ is considerably lower than the K m for Mg 2+ for both enzymes; the maximal rate with Mg 2+ is about the same as with Mn 2+ for the NADP‐dependent enzyme, but only 20% of that with Mn 2+ for the NAD(P)‐dependent enzyme. The possible role of these enzymes in contributing to citrate synthesis by isolated spiny dogfish liver mitochondria is discussed. NAD‐ or NADP‐dependent malic enzyme activity could not be detected in the cytosol. © 1995 Wiley‐Liss, Inc.