BOVINE RETINAL ROD GUANYL CYCLASE REPRESENTS A NEW N-GLYCOSYLATED SUBTYPE OF MEMBRANE-BOUND GUANYL CYCLASES

The molecular properties of retinal rod guanyl cyclase were investigat ed. Peptides were derived from a 112-kDa protein previously identified as the particulate bovine retinal rod guanyl cyclase. The peptides sh owed 100% identity to the deduced amino acid sequence of the cloned hu man retina-specific membrane guanyl cyclase, whereas identity to the m embers of the natriuretic peptide receptor guanyl cyclases was 14-59%. The 112-kDa protein was further purified by a new approach using whea t-germ agglutinin chromatography. This indicated N-linked glycosylatio n in retinal rod guanyl cyclase. N-glycosylation was unexpected from t he sequence of the human retina-specific membrane guanyl cyclase, alth ough it is a common property of natriuretic peptide receptors. Therefo re, we further analyzed the carbohydrate composition of bovine retinal rod guanyl cyclase by lectin binding using the lectins Galanthus niva lis agglutinin, Sambucus nigra agglutinin, Maackia amurensis agglutini n, Ricinus communis agglutinin, Datura stramonium agglutinin, peanut a gglutinin and by chromatography of the purified enzyme using concanava lin-A-Sepharose. The oligosaccharide side chains were of the high-mann ose type or hybrid type, probably with mannose, N-acetylglucosamine an d sialic acid as terminal sugars. Enzymic deglycosylation by N-glycosi dase F was achieved after proteolytic digestion with endoproteinase Gl u-C. Lectins neither influenced the basal nor the stimulated guanyl-cy clase activity at low calcium concentrations: Our results indicate tha t the particulate rod guanyl cyclase represents an unusual new subtype of membrane-bound guanyl cyclases.