Some properties of uridine-5′-diphospho-N-acetylgalactosamine:Hematoside N-acetylgalactosaminyltransferase at early and late stages of embryonic development of chicken retina

Abstract

Some properties of the uridine-5′-diphospho-N-acetylgalactosamine:hematoside N-acetylgalactosaminyltransferase were studied in retina tissue from chick embryos at 7 and 14 days of development. The Vmax was about 6-fold higher in retinas from 14 day embryos than in retinas from 7 day embryos. No differences were found either in the apparent Michaelis constant for both donor nucleotide and acceptor glycolipid, or in the optimal detergent concentration, or in the stability upon storage at −14°C or heating at 50°C. Mixtures of homogenates of retinas from 7 day and from 14 day embryos gave the activity values expected for samples free of effectors diffusible and in excess. From experiments of partial delipidation of retina homogenates and reconstitution with lipid from retina homogenates from one or the other age, no indications were found that the activity was modulated by developmental changes in the lipid environment of the enzyme. Taken together, the results suggest that the increase of activity during development was not due to qualitative changes in the catalytic characteristics of the enzyme.