INHIBITION OF PROLYL 4-HYDROXYLASE BY OXALYL AMINO-ACID DERIVATIVES IN-VITRO, IN ISOLATED MICROSOMES AND IN EMBRYONIC CHICKEN TISSUES

The potency of oxalyl amino acid derivatives as inhibitors of prolyl 4 -hydroxylase was studied in vitro, in isolated microsomes and in chick en embryonic-tissue culture. These compounds represent structural anal ogues of 2-oxoglutarate in which the -CH2- moiety at C-3 is replaced b y -NH-, with or without further structural modifications. The most eff icient inhibitor of purified prolyl 4-hydroxylase was oxalylglycine. I ts mode of inhibition was competitive with respect to 2-oxoglutarate. The K-i value varied between 1.9 and 7.8 mu M, depending on the variab le substrate used. Oxalylalanine inhibited purified enzyme with a K-i of 40 mu M. Other oxalyl amino acid derivatives showed little inhibito ry activity. In microsomes isolated from embryonic chicken bone, oxaly lglycine and oxalylalanine inhibited prolyl hydroxylation with IC50 va lues of 23 and 120 mu M respectively. Dimethyloxalylglycine was not an inhibitor of purified prolyl 4-hydroxylase and only weakly active in the microsomal system, but efficiently suppressed hydroxyproline synth esis in embryonic chicken calvaria and lung. The data suggest that dim ethyloxalyl amino acids are converted into active inhibitors in intact cells, most likely in the cytoplasmic compartment.