Microheterogeneity of arylsulfatase A from human tissues

Abstract

Human arylsulfatase A (cerebroside-3-sulfate 3-sulfohydrolase, EC 3.1.6.8) exhibited microheterogeneity on isoelectric focusing in polyacrylamide gels. Pure urinary enzyme gave 3 bands of activity with pI values of 4.7, 4.8 and 4.9, whereas purified liver enzyme yielded six equally spaced bands from pI 4.4 to 4.9. Detection of enzyme in the gel was made by either methylumbelliferyl sulfate or nitrocatechol sulfate. Crude enzyme preparations from human liver, kindey, placenta, brain and testis showed the six-banded pattern with varying amounts of activity in the different bands. The banding pattern of cultured human fibroblast extracts was distinctive: in addition to activity in the area of Bands 1-6 a sharp band at pI 5.1 was observed with both enzyme stains. This latter band was also present in metachromatic leukodystrophy fibroblast extracts. However, in this case the band did not appear when the specific aryl-sulfatase A stain was used. Enzyme Bands 1, 2 and 3 from urine were isolated by extraction of the gel. The three bands refocused in their initial positions; showed nearly identical enzymatic activities toward methylumbelliferyl sulfate, mitrocatechol sulfate, cerebroside sulfate and ascorbic acid 2-sulfate; and demonstrated equivalent immunological competence by antibody titration. The banding pattern of urinary arylsulfatase A was unchanged with neuraminidase treatment, whereas Bands 4-6 of the liver enzyme were converted to Bands 1-3 by this treatment. It appears that Bands 4-6 are due to sialylation of aryl-sulfatase A but that Bands 1-3 are probably due to some other type of post-ribosomal protein modification.