On the origin of alpha-glucosidase in human urine

alpha-Glucosidase and N-acetylglucosamine-6-sulphatase are the major mannose-6-phosphate glycoproteins in human urine

Most newly synthesized lysosomal enzymes contain a transient carbohydrate modification, mannose 6-phosphate (Man-6-P), which signals their vesicular transport from the Golgi to the lysosome via Man-6-P receptors (MPRs). We have examined Man-6-P glycoproteins in human urine by using a purified soluble fragment of the soluble cation-independent MPR (sCI-MPR) as a preparative and analytical affinity reagent. In a survey of urine samples from seven healthy subjects, the pattern of Man-6-P glycoproteins detected with iodinated sCI-MPR as a probe in a blotting assay was essentially identical in each, regardless of sex or age. Two bands of approx. 100 and 110 kDa were particularly prominent. Man-6-P glycoproteins in human urine were purified by affinity chromatography on immobilized sCI-MPR. Seven distinct bands revealed by SDS/PAGE and Coomassie Blue staining were subjected to N-terminal sequence analysis. The prominent 100 and 110 kDa Man-6-P glycoproteins were identified as N-acetylglucosamine-6-sulphatase and alpha-glucosidase respectively. This identification was confirmed by molecular mass determinations on the two major bands after deglycosylation. Sequence analysis revealed arylsulphatase A and several previously unidentified proteins as minor species. Man-6-P glycoproteins were also purified on an analytical scale to determine the proportion of a number of lysosomal enzyme activities represented by the mannose-6-phosphorylated forms. The lysosomal enzymes in urine containing the highest proportion of mannose-6-phosphorylated form were beta-mannosidase (82%), hexosaminidase (27%) and alpha-glucosidase (24%). The profiles of Man-6-P glycoproteins detected by blotting in urine and plasma were not similar, suggesting that the urinary species are not derived from the bloodstream.

Preparation of monoclonal antibodies against acid alpha-D-glucosidase for study of Chinese glycogenosis type II patients

Two monoclonal antibodies (Mabs), 8-23 and 4-6, against human acid alpha-D-glucosidase were generated to analyse the intracellular alpha-D-glucosidase from seven Chinese Pompe's disease families with the following study design: [1] Purified alpha-D-glucosidase from normal human urine was used as antigen for immunization of mice. [2] The splenic cells of immunized mice were isolated and fused with myeloma cells NS-1 for generation of hybridomas and production of anti-human alpha-D-glucosidase Mabs and detection of presence of the enzyme in skin fibroblasts obtained from the Pompe's disease families and normal controls. [3] Functional assay of acid alpha-D-glucosidase was done. Both generated Mabs were IgG1 with a kappa light chain. Mabs 8-23 and 4-6 can recognize 70 kd (kilodaltons) alpha-D-glucosidase evidenced by radioimmunoprecipitation (RIP). Our results showed that alpha-D-glucosidase did exist in the skin fibroblasts of all seven Pompe's disease patients by RIP and in the hepatic cells by immunohistological study. However, functional assay of alpha-D-glucosidase of the seven patients with Pompe's disease showed that the enzyme function of alpha-D-glucosidase was defective. This finding is at variance with the results of other workers which indicated that the amount of mature enzyme was reduced or totally absent in most of the juvenile and adult Caucasian and South African patients. The discordance may imply that the cause of alpha-D-glucosidase deficiency in Chinese patients is quite different from that in Caucasian and South African patients. This needs further study to clarify.

Development of a radioimmunoassay for human deoxyribonuclease I

A reliable radioimmunoassay (RIA) for human deoxyribonuclease I (DNase I) is described. Using delayed addition of tracer antigen, the method is sensitive (9.5 reproducible and specific. A good parallel relationship was observed between the standard curve and dilution curves for human urine and human pancreatic juice. G-actin, a naturally occurring DNase I inhibitor, caused no change in the immunoreactivity of DNase I. In healthy individuals, aged 11-90 yr, the mean serum DNase I was 18.4 ng/ml (SD 6.7 ng/ml). Increased serum DNase I occurred in patients with acute pancreatitis, renal failure, and in about one-third of patients with various malignant tumors.