The Developmental Formation of Asparaginase in Liver and its Distribution in Rat Tissues

Abstract

An assay is described for the quantitative measurement of asparaginase in crude preparations of rat tissues. Most of the asparaginase is concentrated in the liver, in the cytosol, with a Km of 4.71 X 10^-3M for asparagine. The activity is twice as high in adult female as in male liver; this sex difference develops after the 50th postnatal day. Adult kidney contains significant asparaginase activity (25% of that in liver); fetal tissues contain none. Asparaginase is undetectable in transplanted neoplasias with high glutaminase activity. Asparaginase appears in the liver immediately after birth and rises during the ensuing 5 days. Then, after a week of constancy, it rises again to reach adult values (in the male) on about the 20th postnatal day. Separation from the mother prevents the neonatal rise of asparaginase but not that of other liver enzymes. In 8- to 14-dayold rats an injection of hydrocortisone causes a major rise in the level of asparaginase. The results suggest that the physiological stimulus that promotes the first phase of accumulation of rat liver asparaginase is related to nursing and that adrenocortical secretion, known to increase after the 10th postnatal day, promotes the second phase of accumulation of this enzyme.

Glutamine-Dependent Asparagine Synthetase in Fetal, Adult and Neoplastic Rat Tissues

“…Adult liver extract was unable in direct tests to hydrolyze the small amounts of asparagine synthesized, even though the E. coli asparaginase with its low Km for asparagine could do so. Although appearance of the inhibition in liver after birth roughly parallels the developmental curve for asparaginase in liver [12], we found the tumors to be as inhibitory as adult liver, although they contained little or no aspara ginase activity [12]. The possibility remains, among others, that reaction of the intermediate ß-aspartyl adenylate [8] is affected or diverted by the inhib itor.…”

“…It is of interest that the analogous reactions forming glutamylhydroxamates have in the past been accepted as measures of glutamine synthetase, but most of the glutamyl transferase reaction observed in tissues is catalyzed by an enzyme independent from glutamine synthetase [5,6,9], The physiological counter parts of the reactions forming these aspartyl and glutamyl hydroxamates remain to be discovered. One of these, the aspartyl hydroxylamine trans ferase, shares with asparaginase of rat liver [12] the characteristics of a soluble enzyme that lacks cofactor requirements (table VI) and appears only after birth (table VII). The aspartyl hydroxylamine transferase activity of E. coli may also be referable to asparaginase [20].…”

Regulation of Enzyme Development for Glycerol Utilization by Neonatal Rat Liver

“…The initial fetal increases in the activity of glycerol kinase and glycerol 3-phosphate dehydrogenase occur on the 19th day of gestation when both corticosteroids and thyroxine are probably being secreted [24,25], Adminis tration of these hormones to the fetus in utero does not unequivocally identify either or both as the stimulus for the fetal increases in these enzymes. Fetal glycerol 3-phosphate dehydrogenase activities are stimulated con siderably by administration of hydrocortisone but are also stimulated to a less extent by thyroxine (fig.…”

Teratogenic Effects of <i>L</i>-Asparaginase in Rat Embryos in vitro

“…Moreover, a decrease in the protein synthesis due to the lack of L-asparagine could affect the delicate biochemical balance of organogenesis and produce the teratogenic effects already noted. The possible assis tance of a direct embrvotoxic effect is reinforced by the fact that L-asparaginase does only appear in the rat tissues immediately after birth [McGee et al, 1971], It is an established fact that the visceral yolk sac of embryos aged 9.5-11.5 days is the capture site for exterior proteins and the source of amino acids for the protein synthesis of embryonic and visceral yolk sac cells [Freeman and Lloyd, 1983a]. Some teratogenic agents work by alteration of the trophic function of this mem brane's cells: they can affect the pinocytosis [Freeman et al, 1982] or the lysosomal protein degradation [Free man and Lloyd, 1983b], A toxic effect of L-asparaginase on the yolk sac could be considered responsible for the alteration of the subsequent protein synthesis of the embryo.…”