Relative Growth-Promoting Activity in Tissue Culture of Go-Factors and the Parent Vitamins

Abstract

A number of the co-factors tested (FMN), flavin adenine mononucleotide, (DPN), diphosphopyridine nucleotide cocarboxylase has essentially the same activity as the corresponding vitamin (riboflavin, nicotinamide and thiamine, respectively) in promoting the growth of the mouse fibroblast, in terms of either the effective concentration or the amount of growth obtained. Several vitamin conjugates flavin adenine mononucleotide (FAD), triphosphopyridine nucleotide (TPN), coenzyme A and pyridoxal phosphate) proved significantly less active than the parent vitamin (riboflavin, nicotinamide, pantothenate, and pyridoxal, respectively). The present experiments provide no information as to the degree to which these differences may reflect only variations in cell permeability, rather than partial blocks in the utilization of these specific cofactors, or in their conversion to a more active form. Natural citrovorum factor, however, was somewhat more active than folic acid. Of the vitamin congeners or precursors tested, pyridoxine and pyridoxal were essentially equivalent in activity; nicotinic acid was significantly less active than either nicotinamide or DPN in terms of the amount of growth obtained, although the effective concentrations were of the same order of magnitude; while PABA was wholly inactive as substitute for folic acid. As with the co-factors, the present experiments do not exclude differential cell permeability as the basis of these differences.