The transport of vitamin D in the serum of primates.

"Transcalciferin" (the serum transport protein for cholecalciferol and related substances) of two New World monkeys, Cebus apella and Cebus albifrons, was found to be immunologically identical with the transcalciferin of other monkeys and partially with that of man. In contrast with the alpha-globulin mobility of the transcalciferin of other primates, the transcalciferin of cebus monkey has the electrophoretic mobility of albumin. Most of the serum 25-hydroxycholecalciferol was precipitable with isolated monospecific anti-(human transcalciferin) gamma-globulins but not with anti-(human albumin) gamma-globulins. These results indicate that the transport of 25-hydroxycholecalciferol in the cebus monkey is not due to albumin itself but to transcalciferin with the electrophoretic mobility of albumin. Similar variants of transcalciferin also exist in man.