Measurement of the rate of protein turnover and synthesis in the marsupial Honey possum (Tarsipes rostratus)

Rates of protein turnover and synthesis weremeasured in wild-caught Honey possums (Tarsipesrostratus) in the southwest of Western Australia and comparedbetween males and females with and without pouchyoung. Possums were injected with 50 lg of 15N-glycineand ammonia collected within 24 h was used as the nitrogenend-product in a single-injection protocol. The overallmean rate of protein synthesis measured was 7.7 ±0.5 g kg-0.75 day-1, which falls within the range of valuesreported for other marsupial species. Whole body rates ofnitrogen flux and protein synthesis did not vary significantlybetween males and females with and without young, butfemales with pouch young showed significantly lower ratesof protein synthesis when expressed in relation to metabolicbody size. This difference was no longer apparent, however,if the mass of the females was corrected for theestimated mass of the young in the pouch averaging9.3 ± 1.6 g kg-0.75 day-1 and suggesting that the youngshould not be considered as part of the metabolic body pool.Whole body rates of protein degradation were significantlyreduced in females carrying pouch young, suggesting thatprotein may be being diverted from the pool to milk production.Calculations indicate that the daily fraction of thefemale’s nitrogen synthesis rate that needs to be diverted topouch young to sustain their growth is less than 5%, andmay not be detectable with the current methodology.