THE INCORPORATION OF GLUCOSE INTO α‐1, 4‐GLUCAN PROTEINS OF BOVINE RETINA MEMBRANES 1

—Incubation of bovine retina membranes with UDP‐[ 14 C]glucose resulted in the incorporation of [ 14 C]glucose into endogenous α‐1, 4‐glucan proteins. The transferring system was concentrated in membranes that floated at 0.94 and 1.10 m ‐sucrose when centrifuged in a discontinuous sucrose density gradient and was almost absent in the rod outer segment (ROS) and the 100, 000 g supernatant fractions. The glucan proteins labelled by incubation with the radioactive sugar nucleotide at micromolar concentrations were distinguished in two fractions by their solubilities in trichloroacetic acid (TCA): glucan protein‐I (GP‐I), insoluble in TCA, and glucan protein‐II (GP‐II), soluble in TCA and precipitable by ethanol from the TCA soluble fraction. GP‐I and GP‐II were precipitated by trichloroacetic acid‐phosphotungstic acid (TCA‐PTA). A third fraction, glucan protein‐III (GP‐III) was found when incubations were carried out with UDP‐[ 14 C]glucose at millimolar instead of micromolar concentrations. GP‐III was soluble in TCA and in TCA‐PTA and precipitable by ethanol from the TCA soluble fraction. GP‐II was excluded from a Sephadex G‐200 column and showed a greater size than GP‐I in a Sepharose 2B column. The radioactive residues obtained from the glucan proteins after digestion with pronase were totally included in a Sephadex G‐25 column and were of a greater size than the labelled residues released with salivary α‐amylase. Only radioactive maltose was found after a‐amylase treatment. When membranes containing labelled GP‐I and GP‐II were incubated with unlabelled UDP‐glucose at millimolar concentrations, GP‐I was converted into GP‐II and GP‐III was formed.