Aluminium beverage cans as a dietary source of aluminium.

OBJECTIVE: To examine the possibility that aluminium beverage cans contribute to the dietary level of aluminium. METHOD: The aluminium content of a variety of beverages from aluminium cans and glass containers was measured. RESULTS: The contents of 106 aluminium cans and bottles representing 52 different beverages all had a higher aluminium content than Newcastle tap water at 1.4 mumol/L, ranging as high as 385 mumol/L. Non-cola soft drinks averaged 33.4 mumol/L from cans and 5.6 mumol/L from bottles. Cola drinks averaged 24.4 mumol/L from cans and 8.9 mumol/L from bottles, whereas beer in cans or bottles averaged about 6 mumol/L. CONCLUSIONS: In general, the aluminium content of beverages from aluminium cans was higher than that from glass containers, and it rose with decreasing pH. Within a given category there was a wide variation in aluminium content. If the speculative link between aluminium intake and Alzheimer's disease is established then beverages from aluminium cans, particularly soft drinks, may be a risk factor.

Initiation of replication of the Escherichia coli chromosomal origin reconstituted with purified enzymes.

A mixture of purified proteins has replaced a crude enzyme fraction capable of efficient replication of oriC-containing plasmids. The reconstituted enzyme system contains proteins which provide initiation, replication, and specificity functions required for dnaA-dependent replication specific for an oriC template. Replication can be separated into successive stages of RNA synthesis and DNA replication. Isolation of an intermediate no longer requiring RNA polymerase action requires the presence of dnaA protein, DNA gyrase, dnaB protein and dnaC protein. Intermediate formation likely involves binding of dnaA protein to a 9-bp sequence present 4 times as inverted repeats within the chromosomal origin sequence.

Cryoenzymology and spectrophotometry of pea seedling diamine oxidase.

Diamine oxidase follows bi-ter ping-pong kinetics, with an intermediate, "reduced" free-enzyme form being generated after the anaerobic conversion of amine to aldehyde. Visible spectra of diamine oxidase reacting at subzero temperatures provide evidence that this intermediate enzyme form is obtained via several other intermediates and that the environment of the Cu(II) changes dramatically during the course of the reaction [even though it is not reduced to Cu(I) during the catalytic cycle]. The spectrum of this form of diamine oxidase, which is obtained 0.5--2 h after the addition of amine at -5 to -15 degrees C, is independent of substrate, is identical with that obtained by anaerobic addition of substrate at room temperature, and provides evidence for a direct interaction of Cu(II) with the organic cofactor of the enzyme. This interaction is apparently charge transfer in nature. Upon removal of Cu(II) from the native enzyme, one obtains spectral evidence that the organic cofactor is still present. However, removal of the Cu(II) from the reduced (intermediate) enzyme form yields a featureless enzyme spectrum and a Cu(II)--chelate complex which contains a new ligand, which is presumably the second prosthetic group.

Optimized preparation and determination of pea seedling diamine oxidase.

The level of diamine oxidase in pea seedling stems has been determined as a function of time after germination in both etiolated and non-etiolated plants. The maximum amount of enzyme per plant is obtained between 11 and 13 days. The amount of activity per gram of tissue appears to be proportional to the rate of growth. We describe an efficient method of isolation of pea seedling stem diamine oxidase from 12-day-old etiolated seedlings, a procedure that brings the enzyme to purity after a 97-fold purification. A new assay procedure for pea seedling diamine oxidase is detailed and compared to previously used methods. The kinetic parameters for three common substrates have also been determined. SDS-acrylamide gel electrophoresis, gel filtration chromatography and copper analyses have been used to determine that pea seedling diamine oxidase exists as a dimer of two apparently identical subunits, the dimer molecular weight being about 190,000. The isoelectric point of this enzyme was determined to be 6.5.