Demonstration of Various Acid Hydrolases and Preliminary Characterization of Acid Phosphatase in Naegleria fowleri1

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Abstract
Extracts of the pathogenic ameba Naegleria fowleri, prepared by freeze‐thawing and sonication, were analyzed for their content of various hydrolytic enzymes that have acid pH optima. The organism is rich in acid phosphatase activity as well as a variety of glycosidases which include β‐glucosidase, β‐galactosidase, β‐fucosidase, α‐mannosidase, hexosaminidase, arylsulfatase A, and β‐glucuronidase. The crude extract contained only negligible levels of sphingomyelinase, neuraminidase, or arylsulfatase B. All of the hydrolases exhibited higher activity at pH 5.5 than at 7.0, indicating that they are truly “acid” hydrolases. In general, after centrifugation (100,000 g, 1 h), except for arylsulfatase B, more than half of the activity of each of the various hydrolases was recovered in the supernatant fraction. The acid phosphatase in the high‐speed supernatant was purified 45‐fold (32% yield) by chromatography on QAE‐Sephadex and Sephadex G‐200 and shown to have the following properties: 1) pH optima, 5.5; 2) Km (4‐methylumbelliferyl phosphate), 0.60 mM; 3) molecular weight (estimated by gel filtration chromatography), 92,000; 4) inhibited by heteropolymolybdate complexes but not by L(+) sodium tartrate (0.5 mM) or sodium fluoride (0.5 mM). In addition, unlike the tartrate‐resistant acid phosphatase of Leishmania donovani, the major acid phosphatase of N. fowleri is less than 5% as effective in inhibiting superoxide anion production by f‐Met‐Leu‐Phe‐stimulated human neutrophils. The finding of high levels of a number of acid hydrolases in Naegleria fowleri raises several questions that merit further study: Do the hydrolases perform a housekeeping function in this single cell eukaryote or do they play some role in the pathogenic process that ensues when the organism infects a suitable host?