Identification of Lactate Dehydrogenase Isoenzymes by Rapid Kinetics

Abstract

Stopped-flow kinetics indicate that human and chicken heart-type4 lactate dehydrogenases (LDH) become inhibited as DPNH is oxidized in the presence of high concentrations of pyruvate. This inhibition is much less marked with the human and chicken muscle-type4 enzymes. The initial rates and the difference in inhibition between the two types of enzyme have made it possible to determine the amount of, as well as the ratio between, the two types of LDH that are present in a given sample by a single kinetic assay. The stopped-flow kinetic method has been used to analyze amounts of LDH isoenzyme in different tissues, as well as in serum.Significant kinetic differences exist between chicken heart (H) and chicken muscle (M) lactate dehydrogenase (LDH) (1-3). At high pyruvate concentrations, or after previous incubation with DPN+, the heart enzyme is inhibited to a greater extent than the muscle enzyme (3). Similar differences have been found between the enzymes from human heart and human liver (4).The kinetic behavior of the various isoenzymes of LDH is governed by their subunit composition. Hence, the H2M2 isoenzyme will exhibit kinetics that are almost identical with those of a mixture of equal amounts of H4 and M4 LDH (5).Concentrations of LDH and isoenzyme patterns are important in clinical diagnosis. Vessell and Bearn noted that the isoenzyme pattern of serum changes after myocardial infarction (6). Changes in the isoenzyme pattern are observed as early as 6-12 hr after the initial attack of pain and have been shown, in dogs, to be a more sensitive indicator of myocardial necrosis than total serum activity (7). Changes in LDH isoenzyme patterns are a constant feature in diseases where liver-cell damage occurs (8). Malignancies, hemolytic anemias, and muscular dystrophy will also alter LDH concentrations and isoenzyme patterns of serum (9). The changes are usually evaluated by electrophoretic methods, which are considerably time-consuming. We are reporting a method involving a single assay taking less than a minute that determines the total amount of LDH, as well as the relative concentration of H and M subunits. This method is based on the difference in inhibition of the two different types of LDH at high concentrations of pyruvate. MATERIALS AND METHODSMaterials. Pyruvate was purchased from Calbiochem. DPN+ and DPNH were purchased from P-L Biochemicals.

The energy hypothesis of sleep revisited

“…Lactate dehydrogenase 2 B protein, which is associated with astrocytes (Pellerin et al, 1998) and catalyzes the conversion of pyruvate to lactate (Bishop et al, 1972), is significantly increased in mouse cerebral cortex after 6 hours of sleep deprivation (Pawlyk et al, 2007). Furthermore, glucose transporter 1, associated with epithelial cells of the blood-brain barrier and astrocytes (reviewed in Duelli and Kuschinsky, 2001), shows increased gene expression in rat cerebral cortex following sleep deprivation, and is also increased in spontaneous wakefulness compared to sleep (Cirelli et al, 2004b; Cirelli and Tononi, 2000).…”

Evidence Supporting the Existence of an Activity-Dependent Astrocyte-Neuron Lactate Shuttle

“…In contrast, the LDH1 isoform is preferentially expressed in tissues such as the heart, which are characterized by a more sustained level of activity. The LDH 1 isoform exhibits a lower K m and is inhibited by pyruvate and lactate at relatively low concentrations [Gerhardt-Hansen, 1968;Bishop et al, 1972]. These characteristics render LDH 1 poised to promote the conversion, with high affinity, of a substrate (lactate) into a product (pyruvate) which requires efficient and rapid clearance.…”

Biochemical Markers of In Vivo Hepatotoxicity

“…Although not organ specific, elevated LDH activity indicates tissue damage, and other more specific diagnostic tests may help identify the source. The various isoenzymes of LDH can be identified by electrophoresis and these may also help in identifying the source of tissue damage [39].…”