. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 14 J. A. STUART ET AL low L-BHBDH activity observed in the mitochondrial fraction thus can be attributed to cytosolic contamination. Low D-BHBDH activities in Bradvbaena, Arion, and Archachatina hepatopancreas were likely due to contami- nating i -BHB in the commercial D-BHB preparation (L-BHB contamination was up to 2%). As we used a [o-BHB] of 20 mM in the assays, as much as L-BHB could have been present. Heart and kidney were fractionated in the same way as the hepatopancreas. Fractionation of heart tissue re- sult
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 14 J. A. STUART ET AL low L-BHBDH activity observed in the mitochondrial fraction thus can be attributed to cytosolic contamination. Low D-BHBDH activities in Bradvbaena, Arion, and Archachatina hepatopancreas were likely due to contami- nating i -BHB in the commercial D-BHB preparation (L-BHB contamination was up to 2%). As we used a [o-BHB] of 20 mM in the assays, as much as L-BHB could have been present. Heart and kidney were fractionated in the same way as the hepatopancreas. Fractionation of heart tissue re- sulted in a lower recovery of mitochondria and greater leakage into the cytosol of mitochondrial matrix enzymes (Table I), perhaps because of the small size of these tis- sues (Stagnicola hearts averaged mg; Pomacea hearts averaged 10 mg). Nonetheless, the distribution of BHBDH activity approximated those of CCO and CS in these tissues, indicating that BHBDH activity is localized to the mitochondria in basommatophoran heart and archi- taenioglossan heart and kidney. In all of these tissues, BHBDH was specific for D-BHB, with no oxidation of L-BHB observed. The pattern of D- and L-BHBDH distribution in Archti- chatimi (Table I) parallels that seen in Cepaea. In C. nemoralis tissues, no mitochondrial form of BHBDH was found (5). Instead, a cytosolic L-BHBDH was present in hepatopancreas and kidney, and a cytosolic D-BHBDH was found in heart and kidney. Similarly, D-BHB was oxidized by Archaclmtina heart and kidney homogenates and L-BHB was oxidi/ed by kidney and hepatopancreas. This configuration of BHBDH organization appears to be characteristic of the Stylommatophora. We investigated the evolution of cytosolic BHBDH isoforms by mapping the occurrence of the mitochondrial D-BHBDH and cytosolic L-BHBDH of gastropod hepato- pancreas onto a gastropod phylogeny (8) using the Mac- Clade (9) software program (Fig. 1). Mollusc phylogenies based upon morphological (10) and molecular (8,
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