ABSTRACT
Optimum substrate and co-factor concentrations and pH are given for the assay of cysteine desulphydrase in chick tissues.
Endogenous desulphydrase activity (no added co-factor) was very low in the yolk from 4 — 12 days and in the whole chick embryo from 3 — 8 days of incubation, there was little in the chorio-allantoic membrane or in the brain and heart of older embryos.
Specific desulphydrase activity in the area opaca of blastoderm increased rapidly with development of the yolk sac and was maximal at 7 — 11 days of incubation. Activity had fallen to half the value by 16 days of incubation. There was twice as much activity in White Leghorn yolk sac homogenates than those of Brown Leghorns. There was no deficiency of co-factor in such homogenates.
The desulphydrase of Brown Leghorn livers increased from 7 — 16 days of incubation (per mg. protein) but remained constant during the embryonic development of White Leghorn livers. Livers showed a deficiency of co-factor.
Just before hatching the liver desulphydrase of both breeds begins to decrease and in White Leghorns had decreased to adult level by 1 week after hatching; whereas in Brown Leghorns the rate of decrease was slower. Liver desulphydrase was increased when adult cockerels were fed on a hard-boiled egg diet.
Attempts at enzyme induction by injection of cysteine were generally unsuccessful. When cysteine (16 mg.) was injected at 7 and 10 days of incubation liver desulphydrase had risen by 60 and 100 per cent, respectively 1 day later. Multiple injection of cysteine into young chickens produced only a 40 per cent, increase in liver desulphydrase.
The paucity of evidence in favour of substrate-induced enzyme inductions in embryos is discussed.