TOTAL FOLATE BINDING-CAPACITY OF NORMAL HUMAN-PLASMA, AND VARIATIONS IN UREMIA, CIRRHOSIS, AND PREGNANCY

  • 1 January 1976
    • journal article
    • research article
    • Vol. 48  (6) , 911-921
Abstract
The current study presents evidence that all human serum contains a class of high-affinity folate binders (KA [affinity constant] = 2.8 .times. 1010 (l/m), which migrate as 1 peak on gel filtration. Failure of previous studies to detect this characteristic in all but a minority of subjects is attributable to its variable, often total, saturation. Direct measurement of the total folate binding capacity (TFBC) was made possible by dissociation of endogenous folate-binder complexes at acid pH, removal of free folate by coated charcoal, and radiofolate tagging. This procedure does not appear to significantly denature the binders, which release and rebind similar quantities of 3H-PGA [pteroylglutamic acid]. In 20 normal subjects TFBC ranged from 100-325 pg/ml (mean .+-. SE = 174 .+-. 16), and was always at least 33% saturated. In 3 clinical conditions, all associated with elevated unsaturated folate binding capacity, 3 different patterns emerged when TFBC was also measured. Uremic subjects had significantly elevated mean TFBC with normal saturation. In cirrhotic subjects mean TFBC approximated normal, but saturation was significantly decreased. In pregnancy 2 groups were seen: 1 with increased TFBC and the other with a normal TFBC, some of whom had decreased saturation. Lactobacillus casei serum folate level was about 30 times greater than the TFBC; there was no correlation between the two measurements.