Model lipid membrane permeability to ATP

A model phospholipid membrane separating two aqueous compartments was measured for permeability to 3H-ATP by diffusion. No diffusion lag time was demonstrated but the permeability coefficient was dependent on the ionic composition of the aqueous medium. In 0.1 M NaCl and distilled water the permeability coefficient was 6.78 × 10−7 cm/s and 1.41 × 10−7 cm/s, respectively, while in 0.5 mM MgCl2 it varied from a minimum of 0.25 × 10−7 cm/s to a maximum of 6.87 × 10−7 cm/s, depending on the concentration difference of 3H-ATP across the membrane.In 0.1 M NaCl the diffusion process had an activation energy of 1 kcal/mol while in 0.5 mM MgCl2 it exhibited a saturation characteristic which was attributed to space charge effects within the membrane. In 0.5 mM 2,4-dinitrophenol the permeability of the membrane to 3H-ATP was inhibited.

Galactocerebrosidase deficiency in globoid cell leucodystrophy of late onset

Three children with progressive neurological disease are described in whom there was deficient galactocerebrosidase activity in white cells. Necropsy in one patient showed the neuropathological features of globoid cell leucodystrophy, and it is suggested that these patients suffered from a clinically and genetically distinct late form of Krabbe's disease.

Ceramide-like synthetic amides that inhibit cerebroside galactosidase

Amides resembling ceramide (fatty acyl sphingosine) were synthesized and tested for their effects on rat brain cerebrosidase (galactosyl ceramide beta-galactosidase). The best inhibitor was N-decanoyl dl-erythro-3-phenyl-2-aminopro-panediol, which exhibited a K(i) of 0.4 mm. A Lineweaver-Burk plot indicated that the amide acted as a noncompetitive inhibitor, presumably by attachment to a site other than the substrate-active site. Preincubation did not affect the degree of inhibition, and inhibition was independent of incubation duration; these observations suggest that the inhibitor does not combine with the enzyme irreversibly. Structural variations produced decreased inhibitory activity: loss of one of the hydroxyl groups, replacement of the aromatic side chain with an aliphatic or substituted phenyl group, or isomeric inversion of the 3-hydroxyl group. It appears that the best activity is obtained with a substance most closely resembling natural ceramide. The cerebrosidases of rat spleen, kidney, and liver are also inhibited by the same amide.

Tay-Sachs and other lipid storage diseases

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