The aim of this proposed research is to further investigate the beta-galactosidase (E.C. No. 3.2.1.23 beta-D-galactoside hydrolase) activity in human brain and liver tissue. At least five isoenzymic forms of this enzyme are known to be present in human and other mammalian species. The absence or decrease of activity of one or more of these enzyme components appears to be the primary defect in four lipid storage diseases: generalized gangliosidosis, juvenile GM1-gangliosidosis, Krabbe's disease and lactosyl ceramidosis. Each of these genetic diseases results in the storage of specific galactosyl-terminal glycolipids leading to severe mental and/or motor deterioration and early death. The glycolipids stored in these 4 clinically distinct syndromes are normal body constituents on the pathway of ganglioside and red and white blood cell glycolipid catabolism. A genetic defect, resulting in the decrease of specific beta-galactosidase activity, leads to the storage of GM1-ganglioside, asialo GM1-ganglioside (GA1) lactosyl ceramide and galactosyl ceramide. At least 7 glycolipids terminating in beta-linked galactosyl residues a found throughout the human body: GM1-ganglioside, asialoGM1-ganglioside (GA1), lactosyl ceramide, galactosyl ceramide, galactosyl sphingosine (psychosine), monogalactosyl diglyceride, and monoalkyl-monoacyl-glyceryl-galactoside. These 7 glycolipids will be prepared with a radiactive label on the terminal galactosyl residue using biosynthetic and organic techniques. With these glycolipids as substrates, as well as synthetic (unnatural (beta-galactoside-derivatives, the activity of purified beta-galactosidase fractions will be studied. It is hoped that, by using these natural and synthetic substrates, plus synthetic di-and trisaccharide derivatives of these glycolipids, we will learn more about the substrate recognition pattern of these enzyme components. The relationship, if any, between the purified beta-galactosidase isoenzymes will be investigated through studies of molecular weight, amino acid composition, carbohydrate content, subunit dissociation and chemical and enzymatic modifications. These studies will enable us to better understand the etiology of these 4 diseases and the role of lysosomal enzymes in general.
NIH ExPorter
NIH ExPorter