The levels of iron, zinc, and copper in the tissues of the pregnant rat, on d 12, 19, and 21 after impregnation have been determined and compared with controls. Iron levels decreased considerably in late pregnancy as a result of increased fetal requirements, thus diminishing iron stores in rat tissues, but maintaining the circulating plasma levels. Copper levels increased slightly at midpregnancy, but returned to control levels at the end of gestation. Zinc stores also increased slightly during early pregnancy, yet were decreased at the end of pregnancy, but to a lesser extent than those of iron. The data are explained on the basis of equilibrium between assimilation and fetal needs for copper, a slightly higher demand for zinc with altered equilibrium, and a much altered equilibrium for iron that provokes a dwindling of iron maternal reserves that is not compensated by dietary iron.
A kinetic study of the fl-glucosidase-catalysed reaction of a commercial cellulase preparation from Trichoderma viride is described. The Krn and Vmax values of the fl-glucosidase system were: (a) 0.SmM and 6.6 ~mol/min, respectively, using p-nitrophenyl fl-D-glucopyranoside (pNPG) as substrate; and (b) 2.5 mM and 8.1 ixmol/min, respectively, using cellobiose as subtrate. The glucose effect on initial reaction velocity agrees with a mixed-inhibition pattern. The inhibition constant (Ki) values were, 0.53 and 0.39 mM with p N P G and cellobiose as substrates, respectively. The temperature and pH optima were determined.
The blood and plasma as well as fetal, placental and whole conceptus levels of copper, iron, sodium, zinc, potassium, magnesium and calcium were measured in pregnant rats and their fetuses days 11–21 after conception. Maternal blood and plasma concentrations of these metals did not really change in the period studied. In the fetus, the concentrations of iron, zinc and calcium increased, whereas for the other metals, they remained practically unchanged during fetal development. The net cumulative levels of metals in the whole conceptus increased in parallel with fetal growth for most metals, except for the zinc and calcium concentrations which increased at a higher pace, especially after day 16. It is concluded that these data could only be explained by a balanced increase in fetal drainage from the mother, which does not deeply change the homeostatic maintenance of the maternal circulating metal pools.
The daily copper, zinc, iron, magnesium, calcium, sodium and potassium retention from the diet in rats during the second half of pregnancy have been determined and compared with those of adult virgin male and female rats. Pregnant rats had higher mean magnesium and potassium daily retentions than virgin females. The retention of essential metals changed along the second half of pregnancy towards lower values for copper and magnesium and higher ones for potassium. The net absolute metal retention followed the same trends. All other metals studied showed little global differences versus controls without clearly identifiable trends. The results suggest that metal retention is an adaptative element in maintaining the pregnant rat’s metal supply, as the considerable metal retention in the first half of pregnancy is modulated in the second half according to the actual needs of the maternofetal unit.
Kinetic characterization of the inhibition effect of nickel on glucose-6-phosphate
dehydrogenase (EC 1.1.1.49) (G-6-PD) and glutathione reductase (GR; EC 1.6.4.2)
from Saccharomyces cerevisiae was made. The effect of nickel on G-6-PD activity is consistent
with a mixed-type inhibiton pattern, with a competitive character, since the inequality k(i),(int) > k(i), (slope)
shows an inverse relation between varied substrate concentrations and fractional
inhibition. An inhibition effect of nickel on GR activity, when NADPH is the varied
substrate, is also consistent with a mixed-type inhibition pattern. However, pure competitive
inhibition is found on GR reaction when oxidized glutathione is the varied substrate. This
investigation shows the highest sensibility of GR before the inhibitory effect of nickel, in
agreement with the experimental values of inhibition constants found in this study, where
constants related to the GR system are lower than the ones of the G-6-PD system.
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