Pyruvate Kinase

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Pyruvate kinase, also known as pyruvate phosphorus transfer enzyme, phosphopyruvate kinase, has a molecular mass of 228kDa, and the abbreviation is PK: pyruvate-2-O-phosphotransferase. In the glycolysis system, it is an enzyme that catalyzes the formation of the second ATP reaction. It can generate pyruvate and ATP·ΔGo1=-7. 5kcal from phosphoenolpyruvate pyruvate and ADP. In addition to divalent metal ions (Mg²⁺ and Mn²⁺), monovalent metal ions (K⁺, Rb⁺, Cs⁺) are also needed, which is probably K⁺ physiologically. The molecular weight is about 250,000. It catalyzes the formation of ADP into ATP, which results in the formation of the final product of pyruvate.

Figure 1. Protein structure of pyruvate kinase.

Functions

Pyruvate kinase turns phosphoenolpyruvate and ADP into ATP and pyruvate. It is one of the main rate-limiting enzymes in the glycolysis process. There are two isozymes of M type and L type, and M type has M1. And M2 subtype. M1 is distributed in cardiac muscle, skeletal muscle and brain tissue; M2 is distributed in brain and liver tissues. L-type isoenzymes mainly exist in liver, kidney and red blood cells. After myocardial cell necrosis, PK is released into the blood, and the determination of PK can be used to diagnose myocardial infarction.

Clinical significance

Acute myocardial infarction

PK activity began to increase 2h after the onset of acute myocardial infarction, peaked at 22-24h (3 times the control value), and reached the peak on the second day (4 times the control value); it gradually recovered after 48-72h normal. Increased serum PK activity is highly specific for acute myocardial infarction. In addition, since PK activity starts to rise and returns to normal sooner after acute myocardial infarction, it can be used for the diagnosis of prolonged acute myocardial infarction or re-infarction. However, some people think that PK is not as sensitive as CK, but it is more specific than CK. Because of the short rise time, it is best to supplement other monitoring indicators; others believe that PK is a simple, rapid and reliable indicator for the diagnosis of acute myocardial infarction.

Myogenic diseases

The serum PK activity was significantly increased, reaching 1 to the control value 25 times, the positive rate is >90%. In contrast, in patients with neurogenic diseases (spinal muscular atrophy, muscular atrophic lateral sclerosis, etc.), most people have normal serum PK activity. Therefore, the determination of serum PK activity is of certain value for distinguishing myogenic or neurogenic myopathy.

Blood system diseases

The total activity of PK in red blood cells of patients with congenital non-spherical cell hemolytic anemia is significantly reduced. In other blood diseases such as acute leukemia, erythrocyte leukemia, aplastic anemia, anemia that is not effective in treatment, paroxysmal nocturnal hemoglobinuria, congenital anemia, etc., red blood cell PK activity can be reduced to 50% of the control value.

Deficiency

Genetic defects of this enzyme cause the disease known as pyruvate kinase deficiency. In this condition, a lack of pyruvate kinase slows down the process of glycolysis. This effect is especially devastating in cells that lack mitochondria, because these cells must use anaerobic glycolysis as their sole source of energy because the TCA cycle is not available. For example, red blood cells, which in a state of pyruvate kinase deficiency, rapidly become deficient in ATP and can undergo hemolysis. Therefore, pyruvate kinase deficiency can cause chronic nonspherocytic hemolytic anemia (CNSHA).