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W E Knox

Publications and source records attributed to W E Knox.

At least 37 records · Page 2Linked to original sources
PubMed1972

The quantitative determination of phenylalanine hydroxylase in rat tissues. Its developmental formation in liver.

A sensitive method was developed for determining the phenylalanine hydroxylase activity of crude tissue preparations in the presence of optimum concentrations of the 6,7-dimethyl-5,6,7,8-tetrahydropterin cofactor (with ascorbate or dithiothreitol to maintain its reduced state) and substrate. Tissue distribution studies showed that, in addition to the liver, the kidney also contains significant phenylalanine hydroxylase activity, one-sixth (in rats) or half (in mice) as much per g as does the liver. The liver and the kidney enzyme have similar kinetic properties; both were located in the soluble phase and were inhibited by the nucleo-mitochondrial fraction. Phenylalanine hydroxylase, like most rat liver enzymes concerned with amino acid catabolism, develops late. On the 20th day of gestation, the liver (and the kidney) is devoid of phenylalanine hydroxylase and at birth contains 20% of the adult activity. During the second postnatal week of development, when the phenylalanine hydroxylase activity was about 40% of the adult value, an injection of cortisol doubled this value. Cortisol had no significant effect on phenylalanine hydroxylase in adult liver or on phenylalanine hydroxylase in kidney at any age.

Age Factors↗
PubMed1972

Liver phenylalanine hydroxylase activity in relation to blood concentrations of tyrosine and phenylalanine in the rat.

The plasma concentration of phenylalanine and tyrosine decreases in normal rats during the first few postnatal days; subsequently, the concentration of phenylalanine remains more or less constant, whereas that of tyrosine exhibits a high peak on day 13. The basal concentrations of the two amino acids were not altered by injections of thyroxine or cortisol, except in 13-day-old rats, when an injection of cortisol decreased the concentration of tyrosine. In young rats (13-15 days old), treatment with cortisol increased the activity of phenylalanine hydroxylase in the liver (measured in vitro) and accelerated the metabolism of administered phenylalanine: the rate constant of the disappearance of phenylalanine from plasma and the initial increase in tyrosine in plasma correlated quantitatively with the activity of phenylalanine hydroxylase in the liver. In adult rats, the inhibition of this enzyme (attested by assay in vitro) by p-chlorophenylalanine resulted in a proportionate decrease in tyrosine formation from an injection of phenylalanine. However, the quantitative relationship between liver phenylalanine hydroxylase activity and phenylalanine metabolism within the group of young rats was different from that observed among adult rats.

Animals↗
PubMed1972

Function of arginase in lactating mammary gland.

The potential for a considerable formation of ornithine exists in lactating mammary gland because of its arginase content. Late in lactation arginase reaches an activity in the gland higher than that present in any rat tissue except liver. Occurrence of the urea cycle can be excluded since two enzymes for the further reaction of ornithine in the cycle, carbamoyl phosphate synthetase I and ornithine carbamoyltransferase, are both absent from this tissue. Instead, carbamoyl phosphate synthetase II appears early in lactation, associated with accumulation of aspartate carbamoyltransferase and DNA, consistent with the proposed role of these enzymes in pyrimidine synthesis. The facts require another physiological role for arginase apart from its known function in the urea cycle. Significant activity of ornithine aminotransferase develops in mammary gland in close parallel with the arginase. By this reaction, ornithine can be converted into glutamic semialdehyde and subsequently into proline. The enzymic composition of the lactating mammary gland is therefore appropriate for the major conversion of arginine into proline that is known to occur in the intact gland.

Animals↗
PubMed1972

Cytomorphometry of developing rat liver and its application to enzymic differentiation.

Quantitative stereological methods have been adapted for the measurement of the volume of liver attributable to parenchymal, hematopoietic, and Kupffer cells and for the measurement of the relative and absolute number (per unit volume) of these cell types and the mean volume of the parenchymal cell. These morphological parameters are the main ones for interpreting the biochemical differentiation of liver. Quantitative changes in these parameters, in rat liver between the 15th day of gestation and adult life, are presented. Despite the large number of hematopoietic cells, the parenchymal cells fill more than half of the liver volume between the 15th and 18th days of gestation and 0.85 of the liver volume at term. The fraction of liver volume occupied by Kupffer cells is never more than 0.02; the number of Kupffer cells per cubic centimeter increases less than twofold between fetal and adult life. The mean volume of individual parenchymal cells undergoes a threefold rise during late fetal life, declines in the neonatal period, and doubles between the 12th and 28th postnatal days. With the morphometric data obtained, it is impossible to convert enzyme concentrations (units per gram, determined in homogenates of whole liver) to enzyme amounts per unit volume of parenchymal or hematopoietic tissue or per individual cell of either type. In late fetal liver, only rises in enzyme concentration less than twofold may be attributed to the enrichment of parenchymal tissue at the expense of hematopoietic elements. The sudden upsurge, by more than twofold, of hepatic enzymes of the late fetal cluster (and also of the neonatal and late suckling cluster) reflects rises per parenchymal mass and per parenchymal cell. Thyroxine and glucagon, the administration of which to fetal rats promotes enzyme differentiation in liver, are without appreciable effect on the cytological parameters studied. Hydrocortisone accelerates the involution of hematopoietic tissue in fetal liver. Enzymes that are diminished by prenatal injection of hydrocortisone may be concentrated in hematopoietic cells.

Aging↗