Effects of proteolytic and thermal action on the activity of lactate dehydrogenase isozymes LD-1 and LD-5.
L-Lactate dehydrogenase (LD) catalyzes the interconversion of pyruvate and lactate. Using a spectrophotometric assay to determine LD activity, incubation of rabbit, porcine, and bovine LD-1 and LD-5 isozymes with the protease subtilisin (Carlsberg) gave first-order degradation kinetics. Degradation half-lives were significantly lower for the LD-5 isozymes from the three species when incubated with subtilisin at temperatures from 4 degrees C to 25 degrees C. The energy involved in the degradation process, however, was not different. The activation energy for the conversion of pyruvate to lactate by LD-1 at pH 7.4 was significantly higher than that for LD-5 for all three species examined (P less than 0.005). Thermocalorimetry showed that the LD-1 isozymes have both a higher mean temperature of denaturation and a higher heat uptake during the denaturation process than corresponding LD-5 forms. The results suggest that the LD-5 isozymes in the species studied are more metabolically efficient, whereas the LD-1 forms have greater structural stability.
Capps
G W
GW
Department of Biochemistry and Molecular Biophysics, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
Kline
E S
ES
Brandt
R B
RB
D000818:Animals; D002417:Cattle; D006207:Half-Life; D006358:Hot Temperature / Q000009:adverse effects*; D066298:In Vitro Techniques; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D011489:Protein Denaturation; D011817:Rabbits; D013381:Subtilisins / Q000494:pharmacology*; D013552:Swine; D013816:Thermodynamics; D013997:Time Factors
D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase; D013381:Subtilisins