Characterization of solubilized GlcAT-1 (UDP-GlcA: nLcOse4Cer beta 1-3 glucuronyltransferase) activity from embryonic chicken brain and its inhibition by D-erythro-sphingosine.

Glycolipid glucuronyltransferase activity (GlcAT-1) has been solubilized and characterized from 19-day-old embryonic chicken brain Golgi-rich membranes. The enzyme catalyzes the biosynthesis in vitro of GlcA beta 1-3nLcOse4Cer glycolipid using neolactetraosylceramide (nLcOse4Cer, Gal beta 1-4GlcNAc beta 1-3Gal beta-1-4Glc-Cer) as the substrate. The membrane-bound enzyme shows optimum activity in the presence of neutral detergents such as Triton CF-54, Triton DF-12, and Nonidet P-40. Approximately 60% of the enzyme activity can be solubilized from the Golgi membrane by Nonidet P-40. The solubilized GlcAT-1 activity is inhibited by different salts such as NaCl, NaBr, NaI, and NaOAc, but not by sodium fluoride (up to 0.4 M concentration). Desialyzed alpha 1 acid glycoprotein (SA alpha 1AGP) can be used as a substrate for glucuronyltransferase. Competition studies between glycolipid (nLcOse4Cer) and glycoprotein SA alpha 1AGP) substrates show a mixed type of inhibition. Phospholipids, in particular phosphatidylglycerol, stimulate solubilized GlcAT-1 activity, while D-erythro-sphingosine, a metabolite of glycosphingolipids, is inhibitory (50% inhibition at 0.8 mM D-erythro-sph). These results demonstrate that both phospholipid as well as sphingosine might be involved in modulating glucuronyltransferase activity.

Carbohydrate and hydrophobic-carbohydrate recognition sites (CARS and HY-CARS) in solubilized glycosyltransferases.

Six different glycosyltransferases that are active with glycosphingolipid substrates have been purified from Golgi-membranes after solubilization with detergents. It appears that GalT-4(UDP-Gal:GlcNAc-R1 beta 1-4GalT), GalNAcT-2(UDP-Gal:Gal alpha-R2 beta 1-3GalNAcT) and FucT-2(GDP-Fuc:Gal beta GlcNAc-R3 alpha 1-2FucT) are specific for oligosaccharides bound to ceramide or to a protein moiety. These are called CARS (carbohydrate recognition sites) glycosyltransferases (GLTs). On the other hand, GalT-3(UDP-Gal:GM2 beta 1-3GalT), GalNAcT-1(UDP-GalNAc:GM3 beta 1-4GalNAcT) and FucT-3 (GDP-Fuc:LM1 alpha 1-3FucT) recognize both hydrophobic moieties (fatty acid of ceramide) as well as the oligosaccharide chains of the substrates. These GLTs are called HY-CARS (hydrophobic and carbohydrate recognition sites). D-Erythro-sphingosine (100-500 microM) modulates the in vitro activities of these GLTs. Modulation depends on the binding of D-sphingosine to a protein backbone, perhaps on more than one site and beyond transmembrane hydrophobic domains. Control of GLTs by free D-sphingosine was suggested with the concomitant discovery of ceramide glycanase in rabbit mammary tissues. The role of free sphingosine as an in vivo homotropic modulator of glycosyltransferases is becoming apparent.

Morphological studies on the larval stages of three species of Setaria and Dirofilaria repens.

This paper reports for the first time the morphology of larval stages of Setaria labiato-papillosa. The infective larvae of this species had two circles of small papillae on the cephalic end, 4 papillae for outer circle and 6 for inner circle. The caudal end of S. labiato-papillosa is in digital form with 3 transversally arranged papillae. There are 2 circles of small papillae on the cephalic end of S. leichungwingi and S. equina, 4 for each circle; the caudal terminal of the former species is willow-shaped with 3 pearl-like papillae, and that of the latter is conical shaped with 1 bulbed papilla, 2 slightly protruded papillae at sub-terminal. The anal ratios of all the above 3 species are below 3. Morphology of larval stages of Dirofilaria repens was also primarily described in China. The 3 bulbed caudal papillae of the infective larvae are closely arranged, and the anal ratio being less than 2. A key to infective larvae of 8 species of filaria was worked out according to relevant literature and the present study.

A field survey on the role of low-density microfilaraemia cases in the transmission of filariasis.

In former filariasis endemic areas, where the disease has been basically controlled, a few cases of low-density microfilaraemia remain. A survey was carried out in Deqing County, Zhejiang Province, from September 1981 to 1986 in order to determine whether such cases play a role in the continuation of transmission. The results of parasitological and entomological investigations for two consecutive years revealed that after the implementation of intervention measures, the mean microfilaraemia rate in the population fell to about 0.5% and the mean microfilaria density to about 4.2 mf/60 microliter of blood in previously endemic areas of malayan filariasis. Although there were considerable numbers of An. sinensis biting humans, infective larvae could be found in only two positive mosquitoes out of 5,484 dissected, and no new microfilaraemic cases were detected in the 1983 and 1986 follow-up blood examinations, indicating that transmission had already been interrupted. Two volunteers with a microfilaraemia of 3-5 mf/60 microliter of blood were exposed to two batches of An. sinesis in August 1981. The engorged mosquitoes were dissected eight days later. Even though the infection rate of An. sinensis having fed on low-density microfilaraemic cases was as high as 16.8%, the intensity of infection was extremely low, being 1.1 mf/mosquito. From the transmission dynamics point of view, infected mosquitoes carrying very few infective larvae have no practical significance in the transmission of filariasis. It is suggested that the treatment of persons with low-density microfilaraemia (with 5 mf/60 microliters of blood) in areas with low microfilaria rates (less than 1%) need not to be considered as essential.