A new serum lipoprotein found in many rhesus monkeys.

A new serum lipoprotein was found in about 10 out of 30 rhesus monkeys ($\text{Macaca}\text{mulatta}$) which contained 28% by weight of protein, 42% total cholesterol, 22% phospholipid, and 8% triglyceride. This is in contrast to LDL (which the ten monkeys also contained) which had 24% protein, 46% total cholesterol, 24% phospholipid and 7% triglyceride. An S_{f, 1.063} in KBr of 3.0 to 3.7 and molecular weight of 3.5 – 3.7 million were observed compared to means of 8.1 and 3.0 million for normal rhesus LDL. The lower S_f was caused by its higher density. This new lipoprotein was most easily demonstrated and isolated by preparative ultracentrifugation of all serum lipoproteins at density 1.22 g/ml, followed by 6% agarose gel filtration at 6°. The new lipoprotein appeared as a distinct peak eluting before LDL.