The influence of temperature on thermostability, isoenzyme pattern and reaction kinetics of lactate dehydrogenase from fishes

• Published in: Marine biology 1973-03, Vol.18 (1), p.37-45
• Main Author: Kunnemann, H
• Format: Article
• Language: ger
• Subjects: Freshwater
• ISSN: 0025-3162

Methodological problems complicate investigations on thermostability of lactate dehydrogenase (LDH). It is difficult to demonstrate a correlation between adaptation-temperature (AT) and LDH thermostability. Heat-inactivation characteristics change completely if diluted or undiluted tissue extracts are heated. In purified LDH (purchased from Boehringer, Mannheim, FRG), additions such as casein, bovine-serum albumin, NADH and pyruvate - even in small concentrations - can alter considerably the degree of heat resistance. If LDH activity is measured as a function of experimental temperature (ET) according to the composition of the actual test mixture (e.g. altered pyruvate concentration), a different temperature optimum is found. If tissue extracts containing unpurified enzymes are used, the accompanying substances act on the enzyme and modify its properties. Thus, possible influence of AT on enzyme properties can be concealed (suppressed, over-emphasized). In Idus idus acclimated to 10 degree or 20 degree C, brain, gill, gut and white dorsal muscle reveal identical LDH-iso-enzyme patterns. However, liver-LDH shows a pattern dependent on the AT. A total of 11 bands with LDH activity were found. In 10 degree C fishes, the Isoenzymes 1, 3, 6 and 7 are especially active. However, 20 degree C fishes show marked activity of Isoenzymes 5 and 8, and a reduced activity of Isoenzyme 7. According to their electrophoretic mobility, the particular isoenzymes of LDH of white dorsal muscle of I. idus or Rhodeus amarus can be clearly distinguished. The ATs 10 degree or 20 degree C do not influence the dependence of reaction order on ET; this is not true for the velocity constant.