Catalytic properties of the lactate dehydrogenase isozyme “X” from mouse testis

✍ Scribed by Battellino, Luis J. ;Blanco, Antonio

• Publisher: John Wiley and Sons
• Year: 1970
• Tongue: English
• Volume: 174
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1401740207

✦ Synopsis

Abstract

Lactate dehydrogenase (LDH) isozyme 1 (B~4~), 5 (A~4~), and “X” (Testis or Sperm type) have been partially purified from mouse tissues.

The following studies were carried out on the three isozymes: K~m~ and optimum substrate concentration for pyruvate, α‐oxo‐butyrate, α‐oxo‐valerate, lactate, α‐OH‐butyrate, and α‐OH‐valerate, inhibition by substrate and product, effect of malate, N‐(4‐carboxy‐2‐hydroxyphenyl) maleimide, some citric acid cycle metabolites, urea, trypsin and pH.

The mouse testicular LDH isozyme clearly differs from the common lactate dehydrogenases and from the tesficular isozymes from other species. It shows distinct sensitivity to inhibition by substrate or product whether the direct (pyruvate → lactate) or reverse reactions are studied. There is no effect of increasing concentrations of pyruvate or lactate on the direct reaction, while a clear inhibition by lactate or pyruvate is demonstrated on the reverse reaction. Citric acid cycle metabolites, specially malate and succinate, inhibit the direct reaction catalyzed by the “X” isozyme.

These peculiar characteristics suggest a high degree of specialization for the principal testicular isozyme of lactate dehydrogenase.