On the application of affinity chromatography to turnover studies on the lactate dehydrogenase isoenzymes

Effect of pregnancy on the turnover of lactate dehydrogenase and its isoenzymes in mouse tissues

The turnover characteristics of total protein and of lactate dehydrogenase and its isoenzymes have been determined in several tissues of the mouse during the later stages of pregnancy. Whereas most tissues showed markedly decreased rates of both synthesis and degradation of proteins, the incorporation rate in uterus increased. Significant differences in the extent of isotope distribution between total protein and lactate dehydrogenase and its isozymes were also noted. Overall the concept emerges of a pool of body protein which is responsive to the physiological stresses of pregnancy at the level of both tissue and cellular function.

The turnover of lactate dehydrogenase in skeletal muscle of the mouse. Influence of fibre type and exercise regimen

1. The influence of fibre-type and an exercise regimen on the turnover characteristics of proteins in mouse skeletal muscle has been studied. 2. Exercise induced a weight increase in most individual muscles and a decrease in lactate dehydrogenase activity which was more marked in white muscle than red. The coincident decrease in M-subunit activity was more noticeable in fast-twitch muscles than in slow-twitch types. 3. Exercise caused a considerable and consistent increase in the rate of degradation of total soluble proteins in individual muscles, with turnover being higher in muscles with a high red fibre content. 4. The response of lactate dehydrogenase to exercise varied considerably between individual muscles as indicated by the comparative rate constants for synthesis and degradation. In general, degradation was greater in muscle with a high slow-twitch or red fibre content. 5. Overall, a considerable redistribution of protein resources was observed during this physiological perturbation (exercise) with the main emphasis away from the pool of total soluble protein towards the myofibrillar constituents. Highly individualistic responses in relation to rates of synthesis and degradation were observed for the specific protein, lactate dehydrogenase, in the separate muscle of this animal.

Ontogenic characteristics of lactate dehydrogenase turnover in the mouse

1. In order to investigate the ontogenic and turnover characteristics of lactate dehydrogenase (L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) in the foetal mouse, activities of this enzyme and isoenzyme distributions have been measured during development, and the time sequence of incorporation of radioactive amino acids have been determined during the last weeks of gestation. 2. In the early foetal stages, the enzyme was present with low specific activity and in the form of lactate dehydrogenase-5 in all regions, but a marked increase in specific activity became evident about the seventeenth day of gestation, and was accompanied by the formation of tissue specific patterns of isoenzyme distribution. 3. Measurement of turnover parameters was undertaken by both double-label ([3H] and [14C]leucine) and pulse-chase ([3H]leucine) techniques. Both procedures provided indications that appreciable degradation may occur during embryogenesis, with general proteolysis proceeding at a faster rate than with lactate dehydrogenase, and with higher rates of degradation occurring in foetuses which were smaller than average. 4. This data has been discussed in relation to the regional variation in these characteristics and the significance to studies of growth and differentiation.

The effect of intralysosomal sucrose storage on the turnover of hamster fibroblast lysosomal and Golgi-apparatus enzymes

1. The effect of overloading of hamster fibroblast lysosomes with sucrose on the turnover of lysosomal and Golgi-apparatus enzymes was studied. Arylsulphatase B and UDP-galactose-N-acetylglucosamine galactosyltransferase were chosen as appropriate marker enzymes. The relative contributions of changes in the rates of synthesis and degradation to the increased activities of these enzymes after uptake of sucrose were examined by isotopic-labelling experiments. The effects of sucrose uptake on the degradation of total cellular protein and of the cytoplasmic enzyme, alkaline ribonuclease, were determined for comparative purposes. 2. The rates of enzyme synthesis in the presence and absence of sucrose were compared by pulse-labelling the cells with 14C-labelled amino acids, followed by isolation of purified enzymes and determination of their radioactivity. Sucrose uptake produced increases of 270% and 90% respectively in the rates of synthesis of arylsulphatase B and galactosyltransferase, whereas the rate of synthesis of alkaline ribonuclease was not affected. 3. The rates of degration of the enzymes were estimated by measuring the decay with time of the radioactivity of purified enzymes from prelabelled cells. In the absence of sucrose, the apparent half-lives of arylsulphatase B and galactosyltransferase were about 30 days and 40h respectively. After uptake of sucrose, the half-life of arylsulphatase B decreased to about 10 days and that of galactosyltransferase to 10h. Neither the half-life of alkaline ribonuclease (4 days) nor the rate of degradation of total cellular protein was affected by the uptake of sucrose. 4. These results indicate that the hyperactivity of lysosmal and Golgi-apparatus enzymes after the uptake of sucrose is accompanied by increases in the rates of both synthesis and degradation, and that the increased rates of degradation are insufficient to prevent accumulation of the excess of enzymes synthesized; also that the effects of sucrose uptake are restricted to the vacuolar apparatus.