The lysosomal beta-D-N-acetylglucosaminidase isozymes in human plasma during pregnancy: separation and quantification by a simple automated procedure

Phylogenetic analyses suggest multiple changes of substrate specificity within the glycosyl hydrolase 20 family

Background

Beta-N-acetylhexosaminidases belonging to the glycosyl hydrolase 20 (GH20) family are involved in the removal of terminal β-glycosidacally linked N-acetylhexosamine residues. These enzymes, widely distributed in microorganisms, animals and plants, are involved in many important physiological and pathological processes, such as cell structural integrity, energy storage, pathogen defence, viral penetration, cellular signalling, fertilization, development of carcinomas, inflammatory events and lysosomal storage diseases. Nevertheless, only limited analyses of phylogenetic relationships between GH20 genes have been performed until now.

Results

Careful phylogenetic analyses of 233 inferred protein sequences from eukaryotes and prokaryotes reveal a complex history for the GH20 family. In bacteria, multiple gene duplications and lineage specific gene loss (and/or horizontal gene transfer) are required to explain the observed taxonomic distribution. The last common ancestor of extant eukaryotes is likely to have possessed at least one GH20 family member. At least one gene duplication before the divergence of animals, plants and fungi as well as other lineage specific duplication events have given rise to multiple paralogous subfamilies in eukaryotes. Phylogenetic analyses also suggest that a second, divergent subfamily of GH20 family genes present in animals derive from an independent prokaryotic source. Our data suggest multiple convergent changes of functional roles of GH20 family members in eukaryotes.

Conclusion

This study represents the first detailed evolutionary analysis of the glycosyl hydrolase GH20 family. Mapping of data concerning physiological function of GH20 family members onto the phylogenetic tree reveals that apparently convergent and highly lineage specific changes in substrate specificity have occurred in multiple GH20 subfamilies.

Isoenzyme pattern and partial characterization of hexosaminidases in the membrane and cytosol of human erythrocytes

OBJECTIVES

Hexosaminidase activity is present in lysosomes, plasma membrane and cytosol of many human cells. Plasma membrane and cytosolic hexosaminidase is not well characterized, particularly as regards their isoenzyme forms and their relationship with the lysosomal ones.

DESIGN AND METHODS

Erythrocyte hexosaminidase isoforms were chromatographically separated, characterized and compared to those in the plasma of healthy individuals and in the erythrocytes of a Tay-Sachs patient.

RESULTS

Hexosaminidase isoenzymes were found in plasma membrane and cytosol and were composed of the same alpha- and beta-subunits as the lysosomal and plasma hexosaminidase A and B isoenzymes, though with some structural and kinetic differences. In addition, the cytosol contained a hexosaminidase that is a specific N-acetyl-beta-D-glucosaminidase, the one involved in the removal of N-acetylglucosamine residues O-linked to proteins, named O-GlcNAcase.

CONCLUSIONS

This work provides an additional step in the characterization of hexosaminidases helping better understand their role in non-lysosomal compartments and their involvement in physiological or pathological situations.

Plasma beta-N-acetylhexosaminidase isoenzyme composition and temperature conversion factors

Using the chromogenic substrate 3,3'-dichlorophenylsulfonphthaleinyl-N-acetyl-beta-D-glucosaminide for the activity determination of plasma beta-N-acetylhexosaminidase (Hex), the temperature conversion factors (TCF) offer a highly significant positive correlation with the relative proportion of Hex B isoenzyme (P< 0.001). The calculation of TCF 37 degrees/25 degrees C allows the isoenzyme composition of Hex to be determined quickly and cheaply. The results may be superimposed over those obtained in a previously described method based on the calculation of the enzyme's activation energy using four temperatures. However, the use of TCF 37 degrees/30 degrees C does not appear to comply with the required demands.

The lysosomal N-acetyl-beta-D-glucosaminidase (NAG) isoenzymes in plasma: study of distribution in a general population by a simple routine chromatofocusing procedure

We have adapted for routine analysis a pre-existing method for separating the three major N-acetyl-beta-D-glucosaminidase (NAG) isoenzyme forms--A, B+I1 and I2--by chromatofocusing followed by fluorimetric assay of the enzyme activity. This method combines good resolution, accurate quantification of the different isoenzymes and high reproducibility with an acceptable degree of analytical precision. We have applied it to studying the isoenzyme levels in the plasma of a general population of 417 subjects and have analysed these enzyme activities as functions of age, sex, body mass and declared alcohol consumption. Unlike the levels of unfractionated enzyme, levels of all the isoenzymes were higher in men than in women at all ages except in the 20-29 year group. Isoenzyme I2 showed the greatest sex difference. On the whole, with increasing age, both sexes showed more or less regular increases in plasma levels of all the isoenzymes. We also found significant correlations for the population as a whole with age and with body mass index. The only significant correlation with alcohol consumption was for B+I1 in men.

Enzymes of lysosomal origin in plasma of twin neonates

The levels of some enzymes of lysosomal origin were assayed during days 2 and 5 of life in plasma from 11 sets of twin neonates and from 25 neonates from single pregnancies (13 of weight appropriate for gestational age and 12 small for their gestational age) as controls. The plasma enzyme levels were also determined in the correspondent twin and control mothers 2 days after delivery. N-Acetyl-beta-D-glucosaminidase isoenzymes were assayed after chromatofocusing separation. All the plasma enzyme levels were higher in the group of twin neonates and of their mothers than in the respective control groups with differences highly statistically significant for two enzymes, beta-D-galactosidase and alpha-D-glucosidase. In neonate plasma lysosomal enzymes are increased at the fifth day of life with respect to the second day. Full term control neonates showed the same enzyme trend. For the N-acetyl-beta-D-glucosaminidase the more significant differences concerned the isoenzyme I2-P (pregnancy). The pattern of the lysosomal enzymes in the twins resembled that of neonates of diabetic mothers who had had no insulin therapy. Since lysosomal enzymes are considered to be particularly sensitive indicators of carbohydrate metabolism abnormalities, we conclude that twin pregnancies are more at risk for these abnormalities than single ones.

Preparation of a stable liquid material for calibration and quality control for lysosomal enzymes in plasma. Assay of enzymes of lysosomal origin in plasma, I

Several lysosomal enzymes present in human plasma (N-acetyl-beta-glucosaminidase, beta-glucuronidase, beta-galactosidase, alpha-galactosidase, alpha-L-fucosidase, alpha-mannosidase, beta-glucosidase) were maintained in a fully active state for at least 8 months by the addition of ethylene glycol (300 milligrams final concentration) to freshly prepared plasma and storage at -20 degrees C. Pools of human plasma from healthy humans, stabilized and stored as above, and containing a low, medium or high content of the above enzymes, were used to establish the analytical imprecision (within-run, day-to-day and total imprecision) of the fluorimetric assay. Ten replicates in ten different analytical series, covering a period of two months, were performed. The total imprecision (expressed as coefficient of variation) was in general lower than 10%; in a few cases, particularly plasma samples with a low enzyme content, the total imprecision was 18%. The isozymes A, B, I1, and I2 of N-acetyl-beta-glucosaminidase displayed the same stability upon storage as the unfractionated enzyme. It is concluded that pools of human plasma containing known amounts of lysosomal enzymes, stabilized by the addition of 300 micrograms ethylene glycol and stored at -20 degrees C, are suitable liquid materials for calibration and quality control for the assay of the same enzymes.