Phospholipid metabolism in mitochondria and microsomes of rabbit liver during development

Abstract The protein, total phospholipid, phosphatidyl inositol, sphingomyelin, phosphatidyl choline, phosphatidyl serine, and phosphatidyl ethanolamine concentrations of mitochondria and microsomes have been determined m the liver of −12, −9, 0, +2, +9, and +14-day-old rabbits. The pattern of growth and development of the liver and liver mitochondria and microsomes was demonstrated by increased wet weight of the liver, by increased mitochondrial and microsomal protein concentration per whole tissue, and by increased mitochondrial and microsomal phospholipid phosphorus per whole tissue. The protein concentration per g of wet tissue was observed to increase in both mitochondria and microsomes after birth. The concentration of total and individual phospholipid phosphorus per mg of mitochondrial protein does not change during development and would suggest that the pattern of mitochondrial phospholipids has been established prior to the development interval studied (−12 to +14 days). This observation would suggest that the duplicating machinery for the phospholipids of membranes of rabbit-liver mitochondria has already been developed 12 days before birth. However, this is not true for the microsomes. The concentration of phospholipid phosphorus per mg of microsomal protein showed an increase in the amount of total phospholipid and phosphatidyl choline before birth and phosphatidyl ethanolamine and phosphatidyl inositol after birth. The incorporation of radioactive phosphorus into the phospholipid fractions of mitochondria and microsomes seemed to indicate a relatively constant rate of synthesis during development.