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J W Callahan

Publications and source records attributed to J W Callahan.

At least 73 records · Page 4Linked to original sources
PubMed1976

GM1-ganglioside and lactosylceramide beta-galactosidase from rabbit brain: inhibitor and substrate competition studies.

A rabbit brain beta-galactosidase catalyzes the hydrolysis of synthetic substrates and the natural substrates Gm1-ganglioside, lactosylceramide, and asialo-Gm1-ganglioside. gamma-D-Galactonolactone competitively inhibited hydrolysis of Gm1-ganglioside, lactosylceramide, and MU-galactoside with Ki values of 0.26 mM, 0.13 mM, and 0.77 mM, respectively. From activity plots comparing the degree of inhibition to the inhibitor concentration, a single binding site for each substrate was found. NP-Galactoside inhibited the hydrolysis of Gm1-ganglioside and lactosylceramide, where as Gm1-ganglioside inhibited lactosylceramide hydrolysis. At low substrate concentrations (less than 1 mM), Gm1-ganglioside was hydrolyzed effectively in the presence of NP-galactoside, but at higher concentrations hydrolysis of the latter was preferred. Chloromercuriphenylsulfonic acid and iodoacetate were effective inhibitors of the enzyme, but N-ethylmaleimide was not. The degree of inhibition with chloromercuriphenylsulfonic acid was different for each substrate. At 0.5 mugM chloromercuriphenylsulfonic acid, all activity towards NP-galactoside, 75% towards lactosylceramide, and 25% of the Gm1-ganglioside activity was lost. Two possible models are presented to explain these results. The data favour the presence of multiple active sites in the enzyme.

Animals↗
PubMed1975

Purification of G-M-1-ganglioside and ceramide lactoside beta-galactosidase from rabbit brain.

The major beta-galactosidase of rabbit brain has been purified over 400-fold. The enzyme converts G-M-1-ganglioside; Gal beta-1 yields 3 GalNAc beta-1 yields 4 (NANalpha-2 yields 3) Gal beta-1 yields 4 Glc yields ceramide (G-M-1) into Tay Sachs ganglioside GalNAc beta-1 yields 4 (NANalpha-2 yields 3) Gal beta-1 yields 4 Glc yields ceramide (G-M-2-ganglioside) and ceramide lactoside, Gal beta-1 yields 4 Glc yields ceramide (Gal-Glc-Cer) into glucocerebroside, Glc yields ceramide (Glc-Cer). The enzyme also hydrolyzes the synthetic substrates NPh-Gal and MeUmb-Gal. It is eluted as a single peak from Sephadex G-200 columns when natural and synthetic substrates were used and has an isoelectric point of 6.3. We were unable to resolve activity towards G-M-1-ganglioside and Gal-Glc-Cer by polyacrylamide electrophoresis in two buffer systems. With G-M-1 the pH optimum was 4.3 in acetate buffer and the K-m value 78 mu-M while with Gal-Glc-Cer, a pH optimum of 4.5 and a K-m of 17 mu-M were found. Hydrolysis of both natural and synthetic substrates was inhibited by gamma-D-galactonolactone, D-galactose and lactose. The data strongly suggest that a single beta-galactosidase hydrolyzes all the substrates tested.

Animals↗
PubMed1975

Sphingomyelinases in human tissues. II. Absence of a specific enzyme from liver and brain of Niemann-Pick disease, type C.

Sphingomyelinase was obtained in excellent yield from liver and brain by homogenization with 0.05 M citrate-phosphate buffer, pH 4.5, containing 0.25% Triton-X-100 (v/v) followed by dialysis of the supernatant fluids against 1% glycine. Total recovery of enzyme was slightly less with tissue from Niemann-Pick disease compared with control tissue. Isoelectric focusing of liver and brain extracts was successfully used to resolve several species of sphingomyelinase. Three (I-III) of the five species were partially characterized. Enzyme I (pI 4.6) had a pH optimum of 4.8-5.0 in acetate buffer and a Km value of 0.026 mM. Both sphingomyelinases I and II were the major enzymes, whereas III, IV, and V were found at lower levels. Of the two major species in normal liver and brain (I and II), species I alone persisted in liver from the two cases of type C, while species III, IV, and V were present. In brain, only species II was decreased but the resolution of the brain enzymes was less satisfactory.

Brain↗
PubMed1975

Sphingomyelinases in human tissues. III. Expression of Niemann-Pick disease in cultured skin fibroblasts.

Sphingomyelinase was effectively extracted cultured fibroblasts homogenized in 1% glycine. The average specific activity was 24.6 nmol substrate hydrolyzed per hr per mg protein. Cultured cells from two cases of Niemann-Pick disease type A and one case of type B had markedly reduced enzyme activity, whereas, in type E cells, total activity was twice normal. Sphingomyelinase was resolved by isoelectric focusing into three peaks of activity (I-II), where I and II were the major forms. Species I had a pI of 4.6, II a pI of 4.8, and III a pI of 5.0. All three peaks, although markedly reduced, were present in cell extracts from both types A and B. All species of enzyme in B cells were found at higher levels than in A cells. Cultured cells from a case of type E contained sphingomyelinase I at a level several fold higher than normal, species II was absent, whereas III was found at near normal levels.

Cells, Cultured↗
PubMed1968

Fucosidosis?

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Child, Preschool↗
PubMedDate not supplied

Properties of partially purified goat kidney beta-D-mannosidase.

Lysosomal beta-D-mannosidase (EC 3.2.1.25) was purified 6900-fold from normal goat kidney by serial Concanavalin A-Sepharose 4B and Red A dye ligand affinity chromatography, followed by anion exchange and molecular sieve high performance liquid chromatography. The relative molecular mass of the enzyme was estimated by molecular sieving to be 79,000 +/- 3000. The apparent Km for the synthetic substrate, 4-methylumbelliferyl-beta-D-mannopyranoside, was 2.3-2.8 mM and the sharp, unimodal pH optimum was 5.5. Enzyme activity was inhibited by Hg2+, Zn2+, Ag+, Co2+ and the thiol reactive agent N-ethylmaleimide. The mannose derivatives p-nitrophenyl-beta-D- thiomannopyranoside and p-aminophenyl-beta-D-thiomannopyranoside inhibited enzyme activity and may be of use as immobilized ligands in future attempts to purify beta-D-mannosidase by specific affinity chromatography.

Animals↗