Alzheimer dementia and the aluminum hypothesis

The possible involvement of environmental aluminum in the etiology of Alzheimer disease and of senile dementia of the Alzheimer type is supported by both direct and indirect relationships between some encephalopathies and the abnormal presence of aluminum(III) in human and animal brain tissues. Proposals for further biochemical, toxicological and analytical work are illustrated.

A neutral lipophilic compound of aluminum(III) as a cause of myocardial infarct in the rabbit

Intravenous administration of aluminum(III) in the form of the hydrolytically stable and moderately lipophilic complex acetylacetonate in the rabbit a severe pathological picture, the most significant feature of which is the occurrence of a myocardial infarct.

The role of copper and quaternary structure on the conformational properties of Octopus vulgaris hemocyanin

Some structural properties of Octopus vulgaris hemocyanin have been investigated by fluorescence spectroscopy. The three-dimensional structure of Octopus hemocyanin is remarkably tight, resulting in a deep burial of almost all the tryptophyl residues of the protein. The hemocyanin conformation has been studied in the two main aggregation states (11 S, 50 S) of the protein, and with respect to the presence or absence of copper in the active site. Upon changing the pH of the solution, Octopus hemocyanin in the 50 S aggregation state can assume at least three different conformations. During the transition between each conformation the fluorescence quantum yield changes, but the environment of tryptophans does not change. Dissociation of the protein from 50 S to 11 S strongly enhances its susceptibility toward denaturating agents such as pH or temperature, and modifies the effects of fluorescence quenchers such as acrylamide. Moreover, these effects are more pronounced when copper is removed from the active site. A comparative analysis of the results shows that the subunit-subunit interactions exerted within the 50 S species are more important in the maintenance of the conformational stability than the copper ions present in the active sites. This behavior can be accounted for by the large amount of Ca(II) ions linked to 50 S hemocyanin.

[Ultrastructure of the gills of Carcinus maenas]

In the present paper it is reported the ultrastructure of the gills from Carcinus maenas, showing the different morphology of the epithelium of the anterior, respect to the posterior gills which can justify, according to some biochemical data, a different function mechanism.

Evidence for acetylated amino-terminal residues in hemocyanins

The NH2 amino acid terminals of hemocyanin from Carcinus maenas determined by the cyanate and by the dansyl-chloride methods gave very low yields. This gave values for the molecular weight which were abnormally high compared to those determined by physical methods. Assuming that the NH2 terminals are acetylated, the number of acetyl groups (determined spectrofluorimetrically) accounts for all the amino sugars present in hemocyanin and for the NH2 terminals assuming that the molecular weight of the polypeptide chains was 25,000 daltons.

Properties of the dolichol phosphate: GDPmannose mannosyltransferase of liver microsomes

The reaction of GDP[14C]-mannose with dolichol phosphate (Dol-P) in hepatic microsomes is characterized by an initial brief period of relatively rapid Dol-P-[14C]-mannose synthesis. The time course of this 1--3 min period of rapid synthesis follows approximate first order kinetics. However, the rate of reaction does not decrease to zero as predicted by the kinetics of the initial period of synthesis, but continues instead at a slow, steadily decreasing, rate. Examination of the time course of Dol-P-mannose synthesis for different concentrations of GDP[14C]-mannose revealed that the extrapolated final level of Dol-P-mannose synthesized is increased when the concentration of GDPmannose is raised. These data, plus those derived from studies of the reverse reaction, suggest that the non-linear time course for the synthesis of Dol-P-mannose is due in part to the reaction approaching equilibrium between the forward and reverse reactions. The effects of Mn++ on the time course of the forward and reverse reaction are complex and suggest that the Mn++ complexes of both GDPmannose and GDP are poorer substrates for the enzyme than the free nucleotides. Perturbations of the lipid environment of the microsomal membrane by treatment with phospholipase A, detergent, sonication, or alkaline pH lead to a decrease in the final level of Dol-P-mannose synthesized, but do not affect the time required for half maximal labeling. When the reverse reaction was investigated in phospholipase A-treated microsomes, the final extent of the reaction was also reduced. These data suggest that perturbation of the membrane lipid environment decreases in some undefined way the availability of Dol-P and Dol-P-mannose to enzyme.

The lipid intermediates arising during glycoprotein biosynthesis in liver microsomes

Incubation of liver microsomes with GDP [14C] mannose leads to the formation of lipid-linked derivatives of [14C] mannose, a dolichol phosphate monosaccharide and dolichol pyrophosphate oligosaccharides. Standard procedures for separating these two types of compounds from each other were found to be deficient in that fractions thought to contain only dolichol pyrophosphate oligosaccharides are contaminated with dolichol phosphate mannose. This paper presents a column chromatographic procedure which conveniently separates the products of an 8 min labeling experiment into two components; dolichol phosphate [14C]mannose and a [14C]-mannose containing oligosaccharide which is also lipid bound. When this oligosaccharide is released from the lipid by hydrolysis and chromatographed on Sephadex G-50 or G-15 it gives a single peak with an indicated molecular weight of 1100. However, when this released oligosaccharide is chromatographed on concanavalin A Sepharose it is resolved into two peaks suggesting that there may be 2 oligosaccharide of approximately the same size but different structures. After brief periods of labeling with GDP [14C]mannose (5 s) an additional oligosaccharide of 3 to 4 sugar residues can be found in the dolichol pyrophosphate oligosaccharides fraction. Incubation of liver microsomes with UDP [14C]glucose or UDP[14C]galactose produces oligosaccharide components containing 7--8 sugar residues. Labeling of microsomes with UDP[14C]acetylglucosamine gives rise to three different components, including a lipid bound oligosaccharide containing 3- 5 sugar residues.

Heavy metal hydrolysis of polyisoprenoid-phosphate mono- and oligosaccarides

Mono- and oligosaccharide derivatives of dolichol phosphate can be hydrolyzed by heavy metal, preferably Zn++ at 100 degrees C or 65 degrees C. The reactions follow first order kinetics. The reaction proceeds through hydrolysis of the sugar phosphate bond.

The transfer of galactose from UDP-galactose to endogenous lipid acceptors in liver microsomes

When the microsomal fraction of beef liver is incubated with UDP-[14-C]-galactose in the presence of an inhibitor of nucleotide pyrophosphatase, there is an incorporation of the [14-C]galactose into glycoprotein and into two lipid components, one soluble in chloroform and the other in chloroform/methanol/water (1:1:0.3). Chromatography of the chloroform fraction on DEAE-cellulose or Kieselguhr G gives a single peak with behavior identical to that of dolichol phosphate mannose. Hydrolysis of the chloroform fraction released free galactose. It seems, therefore, that galactose, like glucose, mannose, and N-acetylglucosamine, can be transferred from its respective sugar nucleotide to glycoprotein via dolichol intermediates.