Muscle protein loss in laying House Sparrows Passer domesticus

In a study of female House Sparrows Passer domesticus, it was established that almost all of the lean dry material lost from the flight muscles during the period of egg formation and laying was protein. The two large fractions of muscle protein, the sarcoplasmic and myofibrillar fractions, were measured biochemically. Protein in the myofibrillar fraction, which formed the greater part of the total protein, decreased during the study period. There was no evidence to support the proposal that sarcoplasm in muscle acts as the main reserve of proteins.