Determination of fractional breakdown rate of slow turnover proteins

OBJECTIVE To develop and test a method to measure fractional breakdown rate (FBR) of proteins using deuterium exchange from water. DESIGN 4‐wks old rats weight 77±1g (mean±SE) were grown for 42 days while drinking 8% 2 H 2 O to label free alanine that is incorporated into body proteins. After the labeling period, the rats were given unlabeled water for 21 days to remove 2 H from both body water and free alanine. At this point, rats were sacrificed at 21, 22, 23, and 25 days to follow the rate of decrease in protein bound 2 H‐alanine with time, which represents FBR. RESULTS The decrease in protein bound 2 H‐alanine enrichments over 4 days were modeled to determine the FBR of mixed liver protein (5.00±1.50%/d), heart left ventricle myofibrillar (5.30±0.88%/d) and collagen protein (3.64±0.61%/d), extensor digitorum longus myofibrillar protein (3.27±0.66%/d), soleus myofibrillar (3.35±0.79%/d) and collagen protein (2.99±0.66%/d), patella tendon collagen protein (0.66±0.28%/d), femur bone head collagen (0.93±0.71%/d) and shaft collagen protein (0.46±0.37%/d). CONCLUSION The measured FBR values were slightly lower than the fractional synthesis rates (FSR) reported by others from similar tissues/protein fractions, which was expected as the rats were still growing. This approach using 2 H 2 O and 2 H‐alanine labeling determines FBR in slow turnover proteins. Grant support: NIH R01‐DK038429