Glucogenic amino acid transported to the liver most commonly -

Ans. is 'a' i.e., Alanine o Transport of alanine from muscle to liver (glucose-alanine cycle) has two functions :-Providing substrate for giuconeogenesisTransport of ammonia (NH4+) to liver for urea synthesis.o During the first few days of starvation, there is a rapid breakdown of muscle protein, providing aminoacids for giuconeogenesis. The most important gluconeogenic amino acid is alanineQ (through glucose-alanine cycle). Alanine is released due to increased muscle protein breakdownQ and is transported to liver for giuconeogen-esis (glucose alanine cycle). The other important gluconeogenic amino acid in starvation is glutamine,o After some weeks of starvation, the rate of muscle breakdown decreases due to decreased need of glucose as a fuel for brain which has began using ketone bodies as a source of energy'. However, when the triacylglycerol stores are completely exhaused, muscle proteins once again enter in a stage of rapid depletion due to protein breakdown,o Alanine transport from muscle to liver has an important additional role, beside giuconeogenesis. Because muscle is incapable of synthesizing urea, most of the ammonia formed by protein catabolism is transferred to pyruvate to form alanine by transamination. Alanine is transported to liver where amino group of alanine is removed to form urea and the resulting pyruvate is converted to glucose by giuconeogenesis.o Thus, sources of alanine release from muscle are (i) Degradation of protein (ii) Transamination of pyruvate.o Besides alanine, lactate produced in muscles by anerobic use of glucose, also seves as a substrate for giuconeogenesis - cori cycle or lactic acid cycle