Muscle contraction pyruvate

ATP is an important source of energy for muscle contraction. Pyruvate dehydrogenase phosphate phosphatase is activated by calcium ion, which increases greatly in concentration during exercise. Why is activation of the phosphatase consistent veith the metabolic requirements of muscle during contraction ... 

Interconversion processes (see p. 120) also play an important role. They are shown here in detail using the example of the PDH complex (see p. 134). The inactivating protein kinase [la] is inhibited by the substrate pyruvate and is activated by the products acetyl-CoA and NADH+H. The protein phosphatase [Ibj—like isodtrate dehydrogenase [3] and the ODH complex [4j-is activated by Ca. This is particularly important during muscle contraction, when large amounts of ATP are needed. Insulin also activates the PDH complex (through inhibition of phosphorylation) and thereby promotes the breakdown of glucose and its conversion into fatty acids. 

Ninety-nine percent of the calcinm and 85% of the phosphoms in the body are fonnd in bones, mostly a poorly crystalline hydroxyapatite Caio(P04)6(OH)2. In addition, calcium is involved in blood coagulation and is an intermediary factor between impulses and muscle contraction. Calcium has an activating effect on enzymes such as phosphorylase kinase and pyruvate dehydrogenase (lipoamide)-phosphatase. 

Cells that lack mitochondria (e.g., erythrocytes) or contain mitochondria but under hypoxic conditions (e.g., vigorously and repeatedly contracting muscle) reduce pyruvate to lactate by lactate dehydrogenase (LDH), which uses NADH as a reductant. This reduction regenerates NAD+, which is required for continued oxidation of glyc-eraldehyde 3-phosphate. 

Figure 16.17 Regulation of glycolysis in muscle. At rest (left), glycolysis is not very active (thin arrows). The high concentration of ATP inhibits phosphofructokinase (PFK), pyruvate kinase, and hexokinase. Glucose 6-phosphate is converted into glycogen (Chapter 21). During exercise (right), the decrease in the ATP/AMP ratio resulting from muscle contraction activates phosphofructokinase and hence glycolysis. The flux down the pathway is increased, as represented by the thick arrows.

As exercise begins, the concentrations of ADP and pyruvate will increase as muscle contraction consumes ATP and glucose is converted into... 

C. Release of Ca + triggers actin-myosin reaction, prompting muscle contraction. Neither fear of surgery nor hydrogen ion levels causes concerted muscle contraction. Increased pyruvate/lactate or temperature tends to counteract contraction. 

Pyruvate dehydrogenase phosphate phosphatase is stimulated by Ca. In muscles, the Ca + concentration increases dramatically during muscle contraction. How would the elevated Ca + concentration affect the rate of glycolysis and the citric acid cycle ... 

Most of the newly synthesized ATP that is released into the mitochondrial matrix must be transported out of the mitochondria, where it is used for energy-requiring processes such as active ion transport, muscle contraction, or biosynthetic reactions. Likewise, ADP, phosphate, pyruvate, and other metabolites must be transported into the matrix. This requires transport of compounds through both the inner and outer mitochondrial membranes. 

As discussed in the previous problem, the phosphatase activates pyruvate dehydrogenase, stimulating the rate of both glycolysis and the citric acid cycle. Calcium-mediated activation of pyruvate dehydrogenase therefore promotes increased production of ATP, which is then available for muscle contraction. 

The use of alanine to transport ammonia from skeletal muscles to the liver is another example of the intrinsic economy of living organisms. Vigorously contracting skeletal muscles operate anaerobically, producing pyruvate and lactate from glycolysis as well as... 

In actively contracting skeletal muscle, the rate of glycolysis far exceeds that of the citric acid cycle, and much of the pyruvate formed is reduced to lactate, some of which flows to the liver, where it is converted into glucose (Figure 30.12). 

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