What defines the glycose-alanine cycle?

The glycose-alanine cycle involves the use of branched-chain amino acids (BCAAs) in muscle tissue. In this cycle, the amino acid alanine is produced from the deamination of BCAAs during periods of intense exercise or prolonged fasting. This alanine then enters the bloodstream and is transported to the liver, where it can be converted into glucose through gluconeogenesis. This process is crucial during exercise, as it helps maintain blood glucose levels and provides a source of energy in the form of glucose, which can then be utilized by the muscles and other tissues.

Understanding the contributions of BCAAs in this cycle highlights their essential role not only as energy sources but also in maintaining overall energy balance and metabolic processes during physical activity. This makes option B the correct answer, as it captures the cycle's reliance on BCAAs for producing glucose from pyruvate, through the intermediary formation of alanine.