PCr

Enzymatic Roles and Functionality

• Creatine kinase catalyzes the conversion of phosphocreatine (PCr) and ADP to creatine and ATP.
• The primary source of PCr in the body is derived from the amino acids arginine and glycine.

Creatine Kinase Characteristics

• The cytosolic isoform of creatine kinase favors breaking down PCr in the muscle cytosol to regenerate ATP.

Creatine-Phosphate Shuttle

• The creatine-phosphate shuttle facilitates the transport of high-energy phosphate from mitochondria to cytosol, aiding in ATP regeneration during intense activity.
• This shuttle is necessary to rapidly resynthesize ATP in the absence of oxygen and maintain energy supply during high metabolism.

Energy Dynamics During Exercise

• PCr levels decrease during exercise as it is converted to ATP.
• ATP levels initially drop but are quickly replenished through anaerobic and aerobic mechanisms.

Glycolysis Overview

• The main product of glycolysis is pyruvate.
• Glycolysis produces a net gain of two ATP molecules per glucose molecule.

Adenylate Kinase Functions

• Adenylate kinase helps maintain ATP levels by catalyzing the reversible reaction of ADP and ATP, ensuring a balance in nucleotide levels.

Lactate Production

• Lactate is formed from pyruvate through the enzyme lactate dehydrogenase (LDH).
• Fast twitch muscle fibers, primarily Type II fibers, produce more lactate during high intensity exercise due to their reliance on anaerobic metabolism.
• LDH1-2 is predominantly found in Type I fibers, aiding in lactate processing.

ATP Production in High Intensity Exercise

• The phosphagen system is primarily responsible for ATP production during the first 30 seconds of a short-distance race, providing immediate energy.
• NAD+ is restored during glycolysis to facilitate continued fermentation and ATP production under anaerobic conditions.

Lactate Clearance Post-Exercise

• After exercise, lactate is transported to the liver for gluconeogenesis or can be oxidized for energy in other tissues, contributing to recovery and energy replenishment.

Test your knowledge on PCr (phosphocreatine) and its sources, its role as an energy buffer, the reversible reaction it undergoes with ATP, and the different isoforms of creatine kinase. Learn about the production of PCr in the liver, pancreas, and kidneys, as well as its dietary sources.