Genetic polymorphism of vitamin B12 binding (R) proteins of human saliva detected by isoelectric focusing.

Genetic polymorphism of the vitamin B12 binding (R) proteins of parotid saliva is determined by autosomal inheritance of codominant alleles. This hypothesis is supported by studies in 43 families including 152 children. For randomly collected salivas from 143 whites, 104 blacks, and 75 Chinese, gene frequencies are as follows: for whites, Rs1=0.88, Rs2=0.12; for blacks, Rs1=0.94, Rs2=0.06; for Chinese, Rs1=1.00. This genetic marker is also shared by R proteins of milk, tears, and leukocytes. In the Rs 1--2 salivary type there is less labeling of the protein products of Rs2 v. Rs1 with 57Co B12 as assessed by the intensity of the bands on the autoradiogram. There is no evidence for close linkage (theta less than 0.01) between Rs and TC II (transcobalamin II) or between Rs and salivary protein locus Pr, Db, Gl, or Ps.