Abstract
According to some papers, most of the labile protein in the body takes the form of flavoprotein. When the labile protein is increased in the body, the excretion of riboflavin in the urine decreases.
The authors studied the relationship between the excretion of riboflavin in urine and the nitrogen reserve under certain amounts of protein administration, on subjects in various states of protein depletion. Prior to and throughout the experiment, 10 mg. of riboflavin was administered every day, thus saturating the subjects with riboflavin.
The experiments were performed, using as subjects, four male students, who, for one week, received a standard diet which contained daily 1.25 g. of protein per kg. of body weight. The diet of the subjects was then changed to either 40 g. of protein or 25 g. of protein or 0 g. of protein per day for a stipulated period. After maintaining the nitrogen equilibrium at each of these periods, 20 g. of whole egg protein were administered to the subjects. Every day the riboflavin excretion in the urine was determined. Most of the periods of protein nutrition were for approximately one week.
Results were as follows :
1. The riboflavin retention in the body increased when an excess of protein was administered and the retention of nitrogen per gram of excess protein which had been administered showed a negative correlation with absorbed nitrogen from the administered diet. The one exception was the protein free diet. The riboflavin retention showed a positive correlation with protein retention, but 0 g., 3.6 g. and above 5 g. per day of absorbed nitrogen showed different correlations, respectively.
2. The authors discussed the probability of flavoprotein being the greater part of labile protein and that flavoprotein works functionally as the reserve protein in the body which regulates the protein metabolism, in accordance with the change of protein intake.
