Studies on biosynthesis of coenzyme A in vitro by rat tissues.

THOUGH the biosynthesis of coenzyme A in microbial systems has been
studied extensively, the biosynthesis in animal tissue preparations does not appear
to have been investigated in detail (cf. Brown, 1959). No appreciable synthesis has
as yet been reported in mammalian tissues in vitro, except in rat brain by Trufanov
and Popova (1956). The occurrence of degradative enzymes and of cysteine desulfhydrase
(Smythe, 1942) in mammalian tissues present obstacles, as there is rapid
destruction of the endogenous as well as newly formed coenzyme A by the degradative
enzymes and the cysteine desulfhydrase limits the availability of cysteine in
the system. The report of hydroxylamine inhibiting the activity of cysteine desulfhydrase
and its use in systems for the biosynthesis of glutathione from the component
amino acids (Kasbekar, 1957) suggested the possibility of its use in following
the biosynthesis of coenzyme A.
The coenzyme A in blood appears to be localized mostly in the cells and no
measurable amount is present in plasma (authors' observation with rat blood ;
Kaplan and Lipmann, 1948. for human blood). There is also no evidence to indicate
the permeability of erythrocyte membrane to coenzyme A of surrounding
medium, and therefore, the hepatic origin of erythrocyte coenzyme A appears to be
a remote possibility. Since erythrocytes have been shown to synthesize lipids
(James et al., 1959 ; Rowe et al., 1960) and heme (London et al., 1950 ; Shemin
et al., 1950 ; Dresel and Falk, 1956 ; Kassenaar et al., 1957) and to acetylate
p-aminobenzoic acid (Blondheim, 1955) all of which require the participation of
coenzyme A, it is to be expected that coenzyme A is a normal component of erythrocytes.
These observations suggest the possibility of de novo synthesis of the
coenzyme in erythrocytes. The ability of blood cells to synthesize other cofactors,
e.g. flavin adenine dinucleotide from riboflavin (Klein and Kohn, 1940), pyridine
nucleotides from nicotinamide (Leder and Handler, 1951), cocarboxylase from
thiamine (Wooley, 1951) and citrovorum factor from folic acid (Mitbander and
Sreenivasan, 1953) is also known.
The biosynthesis of coenzyme A in vitro in liver homogenates, liver slices,
brain homogenates and erythrocytes have been attempted and observations relating
to the kinetics of the biosynthesis, the precursorial efficiency of various sulfhydryl
compounds and the changes observed in these in pantothenic-acid deficiency are
presented.