Properties of the testicular lactate dehydrogenase isoenzyme

Abstract

1. Studies were carried out with pure lactate dehydrogenase isoenzymes C4 (LDH isoenzyme X), B4, (LDH isoenzyme 1) and A4 (LDH isoenzyme 5) isolated from mouse testis, heart and muscle tissue respectively; with LDH isoenzyme X purified from pigeon testes and with crude lysates of spermatozoa from man, bull and rabbit. 2. LDH isoenzyme X from all species showed greater ability than the other isoenzymes to catalyse the NAD+-linked interconversions of 2-oxobutanoate into 2-hydroxybutanoate and of 2-oxopentanoate into 2-hydroxypentanoate. 3. Mouse LDH isoenzyme X presented the broadest spectrum of substrate specificity. It exhibited very similar Km values for a variety of 2-oxo acids: 2-oxopropanoate (pyruvate), 2-oxobutanoate, 2-oxo-3-methylbutanoate, 2-oxopentanoate, 2-oxo-3-methylpentanoate, 2-oxo-4-methylpentanoate, 2-oxohexanoate and 2-oxo-3-phenylpropanoate (phenylpyruvate). The corresponding 2-hydroxy acids were also readily utilized in the reverse reaction. A strong inhibition by substrate and product was demonstrated for the direct reaction. 4. Intracellular distribution of LDH isoenzyme X was investigated in mouse testes. LDH isoenzyme X activity was located in the fraction of “heavy mitochondria” and in the soluble phase. 5. A possible functional role for LDH isoenzyme X is proposed: the redox couple-2-oxo acid-2-hydroxy acid could integrate a shuttle system transferring reducing equivalents from cytoplasm to mitochondria.

Expression and Characterization of a Murine Enzyme Able to Cleave β-Carotene

“…5A), showed a major protein species that copurified with the dioxygenase-GST fusion protein bound to glutathioneSepharose. MALDI-MS analysis of the protein excised from the SDS-PAGE gel identified the protein as an atypical testisspecific LDH-C. LDH-C was originally identified in the 1960s and demonstrated to catalyze the reversible oxidation of lactate and other secondary alcohols (45,46). However, the physiologic role of this enzyme has often been questioned because the other widely distributed lactate dehydrogenase species (LDH-A and LDH-B) are both highly expressed in the testis (45,46).…”

“…MALDI-MS analysis of the protein excised from the SDS-PAGE gel identified the protein as an atypical testisspecific LDH-C. LDH-C was originally identified in the 1960s and demonstrated to catalyze the reversible oxidation of lactate and other secondary alcohols (45,46). However, the physiologic role of this enzyme has often been questioned because the other widely distributed lactate dehydrogenase species (LDH-A and LDH-B) are both highly expressed in the testis (45,46). We are unable to find in the literature any information as to whether LDH-C will catalyze either the oxidation or the reduction of aldehydes like retinal, the product of ␤-carotene cleavage.…”

Exogenous lactate is essential for metabolic activities in isolated rat spermatocytes and spermatids

“…It has been shown that testicular LDH-X catalyses preferentially lactate oxidation and is localized in cytosol and mitochondria (Blanco, Burgos, Gérez de Burgos & Montamat, 1976;. This, as well as the localization of mitochondria in early round spermatids close to the cell surface (Clermont & Rambourg, 1978) (Palombi et al, 1979 (Donahue & Stern, 1968 (Biggers, Whittingham & Donahue, 1967;Zeilmaker & Verhamme, 1974;Hillensjö, Hamberger & Ahrén, 1975;Eppig, 1976), but growing oocytes can survive in the absence of pyruvate when cultured in the presence of follicular granulosa cells (Baran & Bachvarova, 1977;Eppig, 1977;Bachvarova, Baran & Tejblum, 1980 …”

Phosphoglycerate Kinase B from Ram Testis

“…Any variation in phosphoglycerate kinase activity to the extent shown by lactate dehydrogenase C, with respect to the A, or B4 isoenzymes [I 51 could severely restrict carbohydrate metabolism in the sperm. Because of its substrate variability lactate dehydrogenase may be involved in a reducing equivalents shuttle [37].…”