12 Activator Proteins for Sphingolipid Hydrolysis

Abstract

Publisher Summary This chapter focuses on the various activator proteins used for the sphingolipid hydrolysis. Mraz et al. found that human hepatic activator protein that was specific for stimulating the hydrolysis of galactosylceramide sulfate by human enzyme could also stimulate the same reaction catalyzed by acidic sulfatases isolated from various invertebrates, including Tethya aurantium (Porifera), Patella vulgata (Mollusca), Maja squinado (Arthropoda), Marthasterias glacialis (Echinodermata), and Microcosmus sulcatus (Tunicata). Thus, the effect of the human activator protein is not restricted to stimulation of human arylsulfatase A. Activator protein was also isolated from Gaucher spleen, in which an extract of homogenized spleen was acidified to pH 4.4, the precipitate removed, and the protein precipitated from concentrated supernatant by ethanol. The fractionation and purification of the activator protein revealed the existence of multiple activators in Gaucher spleen. The major activator substances from both Gaucher and control spleens appeared to be homogeneous when judged by (a) a single band of protein when subjected to both regular and SDS-polyacrylamide disc gel electrophoresis; (b) a single and symmetrical peak of protein coincident with the stimulatory activity during gel filtration on Sephadex G-150; and (c) a linear relationship of 1n Y versus R 2 during equilibrium centrifugation, where Y was the concentration and R the radius. The activator substances from control and Gaucher spleen were similar in that they were both low-molecular-weight proteins. Equilibrium ultra-centrifugation analysis suggested that the activator protein from the normal spleen had a molecular weight of 8803, while that from Gaucher spleen had a molecular weight of 11,044. The activator proteins were small, acid-soluble proteins, and they were not fixed in SDS-polyacrylamide disc gels by a solution containing 10% acetic acid and 25% isopropyl alcohol.