Enzymatic determination of galactosylceramide galactosidase in tissues by NAD cycling

Characterization of 6-hexadecanoylamino-4-methylumbelliferyl-beta-D- galactopyranoside as fluorogenic substrate of galactocerebrosidase for the diagnosis of Krabbe disease

6-Hexadecanoylamino-4-methylumbelliferyl-beta-D-galactopyranoside (HMGal) has been shown to be a specific fluorogenic substrate of galactocerebrosidase and to facilitate the simple enzymatic diagnosis of Krabbe disease in human patients and in twitcher mice. HMGal hydrolysis at pH 4.5 is optimally stimulated by sodium taurocholate (0.25%) and oleic acid (0.05%) with a Km of 0.150, 0.04 and 0.03 mM, respectively for control mouse kidney, human fibroblasts and leukocytes. In control samples, the specific activity (nmol/mg prot./h) for HMGal is higher than for the natural substrate, galactocerebroside, and is severely deficient in the twitcher mouse and in patients with Krabbe disease. Comparative investigation of galactocerebrosidase activity in fibroblasts, leukocytes and brain with radioactive and fluorogenic substrates reveals a good agreement between the results of the two methods. Galactocerebroside (Gal-Cer) is a competitive inhibitor of HMGal hydrolysis in mouse kidney homogenates while GM1-ganglioside has no inhibitory effect in the same assay system. The sensitivity and specificity of this fluorogenic substrate for galactocerebrosidase provides a simple and rapid method for the diagnosis of Krabbe disease, and for the purification of this enzyme from normal tissues.

Increased sensitivity of an enzyme-amplified colorimetric immunoassay for protein A-bearing Staphylococcus aureus in foods

A modification to the enzyme amplification system described by Self (1984), has been developed in which the addition of semicarbazide hydrochloride increased the sensitivity of detection of protein A-bearing Staphylococcus aureus in foods from 4-6 X 10(3) to 20 colony forming units (c.f.u.) g-1 or ml-1. This may be due to the removal of acetaldehyde produced as a by-product of the amplification cycle thereby permitting further cycling to proceed.