an improved method for synthesizing and purifying pgb x , a mixture of lymers of prostaglandin b 1 . pgb x activity is assayed by measuring the minimum amount of pgb x required to restore complete phosphorylation ability to isolated rat liver mitochondria , first aged and degraded to the point where they exhibit less than 5 % of the phosphorylating ability of normal mitochondria . a higher and more reproducible yield of pgb x of improved quality have been produced thereby .