Role of pH in determining the cell-type-specific residual activity of glucocerebrosidase in type 1 Gaucher disease.

Abstract

The properties of control and 370Asn --Ser glucocerebrosidase, the frequently encountered mutated form of the enzyme in type 1 Gaucher disease, were studied in vitro as well as in situ.The catalytic properties of purified 37Asn -* Ser glucocerebrosidase were highly dependent on the assay conditions. The enzyme was deficient in activity towards substrate and in reactivity with the irreversible inhibitor conduritol B-epoxide (CBE) when activated by the bile salt taurocholate. In the presence of more physiological activators, the lysosomal activator protein saposin C and phosphatidylserine, the 37OAsn --Ser enzyme was near normal in kinetic properties at pH values 5, but not at higher pH.In intact fibroblasts, the enzymic activity of the 370AsnSer glucocerebrosidase and its reactivity with CBE were found to be clearly deficient. However, in intact lymphoblasts from the same patients, the behavior of the mutant enzyme was near normal. The catalytic efficiency of 370Asn --Ser glucocerebrosidase in situ was also found to be highly pH dependent. When intact lymphoblasts were cultured in the presence of permeant weak bases, which increase the pH of acidic intracellular com-

Lipids regulate the hydrolysis of membrane bound glucosylceramide by lysosomal β-glucocerebrosidase

“…Concentrations of BMP and other lipids in the lysosomal compartment may vary tremendously between different cell types, and also between lysosomes of one and the same cell due to local fluctuations between influx rates into individual lysosomes and catabolic rates of lipids within individual lysosomes. Local lysosomal conditions may be even more critical for some mutant lysosomal hydrolases, e.g., for mutant GBA1 (89). In Niemann-Pick type C disease, characterized by the cholesterol primary storage, GlcCer secondary accumulation could be triggered by SM secondary accumulation.…”

Discrepancies between genotype and phenotype in hematology: an important frontier

“…The pH of the lysosome is important in determining the activity of a least one common glucocerebrosidase mutant protein; its activity is nearly normal at pH 5 but declines markedly when the pH is lowered. 42 Thus, some of the variability characteristic of this disease might be attributable to individual differences, hereditary or environmental, in the pH of lysosomes.…”

Functional analysis of 13GBAmutant alleles identified in Gaucher disease patients: Pathogenic changes and “modifier” polymorphisms

“…The differences in results do not seem to be due to the method used, since a range of results were reported for the same method. It was suggested that the low activity of the N370S mutant enzyme may depend on the pH of the assay [Vanweely et al, 1993]. However, we tested the N370S enzyme activity at several pH values without finding significant differences in its maximal activity between pH 5.0 and 5.7.…”