Enzymic conversion of 3-hydroxanthranilic acid into cinnabarinic acid by the nuclear fraction of rat liver

1. An enzyme solely localized in the nuclear fraction of rat liver was found to convert 3-hydroxyanthranilic acid into a red product that was isolated and crystallized from the reaction mixture. The product was identified as cinnabarinic acid (2-amino-3-oxo-3H-phenoxazine-1,9-dicarboxylic acid) by comparing its properties with synthetic cinnabarinic acid. 2. The enzyme had optimum pH at 7·2. Heavy-metal ions like Ag⁺, Hg²⁺, MoO₄²⁻, Fe²⁺ and Cu²⁺ were inhibitory; Mn²⁺ activated the reaction to a considerable extent. 3. The reaction was inhibited by mercaptoethanol, GSH and cysteine, and activated by p-hydroxymercuribenzoate and sodium arsenite, which may suggest the involvement of disulphide groups in the reaction.     

Amino acid incorporation by preparations from the developing rat brain

1. A study has been made of the ability of cerebral microsome-cell sap systems, taken from rats at various ages, to incorporate [(14)C]valine. 2. The systems appear to follow Michaelis-Menten kinetics when cell sap is considered as substrate, microsomes as enzyme and total counts/mg. of microsomal protein as a measure of reaction velocity. 3. Reproducible ;affinity constant' values are obtained, and the system from 4-day-old rats has a higher V(max.) and affinity constant than the system from adult rats. 4. It is suggested the the amino acid-incorporating ability of different systems may be compared by this means.     

Phosphoprotein phosphatase activity of rat liver nuclear membrane.

Nuclear membranes from rat liver contain a phosphoprotein phosphatase activity capable of dephosphorylating endogenous nuclear membrane phosphoproteins. This activity was also expressed towards the ³²P-labeled exogenous phosphoprotein substrates phosvitin and lysine-rich histone. Differential effects of altered ionic strength, EDTA, pyrophosphate, and 2-mercaptoethanol on the phosphatase activity towards the two exogenous substrates suggest the presence of multiple phosphatases in the nuclear membrane. ATP, ADP, and sodium fluoride inhibited activity towards both exogenous substrates, while cyclic AMP or cyclic GMP at 10^?6M had no apparent effect.     

Amino acid transport in plasma membrane vesicles from isolated rat liver parenchymal cells

Plasma membrane vesicles were prepared from isolated rat liver parenchymal cells. The transport of several amino acids was studied and found to be identical to that in membrane vesicles from whole liver tissue.     

Changes of nuclear membrane fluidity during rat liver regeneration.

We have previously shown that the nuclear membrane fluidity is affected by lipid composition changes and that is very high, particularly in the hydrophobic core. The aim of this work is to study the modifications of nuclear membrane fluidity in relation to the cell cycle. Since compensatory hepatic growth is an informative and well characterised model for natural cell proliferation, the nuclear membrane fluidity, detected by two fluorescent probes, was studied at various regenerating times, ranging from 0 to 30 hours after partial hepatectomy. At 18 hours after partial hepatectomy the nuclear membrane fluidity increased and at 30 hours the higher values of hydrophobic core fluidity were observed. The behaviour of fluidity was related to the nuclear membrane neutral-sphingomyelinase activity and, then, to the content of sphingomyelin. Therefore, the significant changes of the nuclear membrane fluidity and of the neutral-sphingomyelinase activity found during rat liver regeneration suggested a their likely role in signal transduction pathways implying cell regeneration.