[Evaluation of hyperuricemia caused by fructose in a status of altered uric acid metabolism]. / Valutazioni sull'iperuricemia da carico di fruttosio in condizioni di alterato metabolismo dell'acido urico.

It's reported that oral administration of fructose in normal and gouty patients causes a rise in serum uric acid (see "References": Stirpe et al.). The changes in serum uric acid after administration of fructose to gouty patients and to children of gouty patients were significantly different from the changes observed in normal subjects, both for the extent and for the duration of hyperuricaemia. In this study the authors verify if the fructose-induced hyperuricaemia can help to identify gouty patients from people with different metabolic alteration of serum uric acid levels (i.e. chronic leukaemias and some neoplastic diseases).

Biosynthesis of immunoglobulin A (IgA). Secretion and addition of carbohydrate to monomer and polymer forms of a mouse myeloma protein.

Cell suspensions of mouse plasma-cell tumour MOPC 315 secreting predominantly IgA (immunoglobulin A) monomer and dimer were incubated with radioactive leucine, mannose, galactose and fucose for various periods of time. The amounts of secreted and intracellular immunoglobulins were measured by co-precipitation with specific antibody, and the molecular species present were assessed by electrophoresis in polyacrylamide gels. Analysis of the secreted myeloma protein demonstrated that monomer and dimer IgA molecules are identical with respect to carbohydrate composition and rate of secretion. Within the cell, the myeloma protein is almost entirely accounted for by monomer units which either leave the cell as such or are polymerized with the addition of J chain close to the time of secretion. The results support the concept of a stepwise addition of carbohydrate residues to IgA immunoglobulin during the process of secretion. Similar patterns of carbohydrate assembly were found for the monomer or dimer molecules. Mannose residues are added at an early stage, whereas fucose is added close to the time of secretion. Galactose is also added early, but some may also be incorporated at a later stage. Control of IgA polymerization is considered unlikely to reflect regulation at the level of carbohydrate addition, and it is suggested that the critical controlling factor is the J chain.

Biosynthesis of immunoglobulin A (IgA) and immunoglobulin M (IgM). Requirement for J chain and a disulphide-exchanging enzyme for polymerization.

Mouse myeloma cells secreting 19S IgM (immunoglobulin M) (MOPC 104E and TEPC 183) or monomer and polymer IgA (immunoglobulin A) (MOPC 315) were incubated with radioactive leucine and the intracellular and secreted immunoglobulins and immunoglobulin subunits were prepared by preparative sucrose-density-gradient centrifugation. Samples were reduced in the presence or absence of isolated J chain, passed over Sephadex G-25 and then incubated at 37 degrees C for 30min with or without a source of disulphide-interchange enzyme. The extent of reassembly of reduced subunits was then evaluated by electrophoresis in polyacrylamide gels. Provided that J chain and the disulphide-interchange enzyme were supplied, both IgM and IgA could be assembled from their respective subunits, obtained by reductive cleavage of polymeric forms. Under similar conditions, assembly of polymeric forms from intracellular or secreted 7S monomer subunits also occurred. Under these conditions polymerization was total, there being no residue of the monomeric form. Reassembly did not occur in the absence of either J chain or the enzyme. All of the J chain released from IgM by reductive cleavage was incorporated back into the reassembled polymer. The J chain is therefore likely to be an essential structural requirement for polymeric immunoglobulins. A variety of controls ruled out non-specific interactions, and further suggested that the amino acid sequence of polypeptide chains determines the specificity of polymerization. The fact that intracellular IgA and IgM monomer subunits known to be deficient in galactose and fucose can be completely polymerized suggests that the addition of carbohydrate does not control polymerization.

Biosynthesis of immunoglobulin A (IgA) and immunoglobulin M (IgM). Control of polymerization by J chain.

Cell suspensions of mouse plasma-cell tumours secreting IgA (immunoglobulin A) and IgM (immunoglobulin M) were incubated with radioactive leucine for various periods of time. The secreted immunoglobulins were precipitated from the culture medium with specific rabbit antisera to determine the relative distribution of radioactivity among the different molecular species, and to estimate the fraction of total radioactivity in the J chain. For IgM-secreting cells there is a balanced synthesis of 7S subunits and J chains, and the secreted product is uniformly assembled to the pentamer. In cells secreting IgA, however, the results demonstrate that the pool of intracellular J chain is less than the intracellular IgA pool. The concentration of J chain is therefore limiting and is less than the requirement for complete polymerization. The major factor that determines whether an intracellular monomer is secreted as such or is polymerized with the addition of J chain is therefore the amount of intracellular J chain. When this is limiting, as it is in cells secreting IgA, then monomer will be secreted.

The regulation of rat liver xanthine oxidase. Involvement of thiol groups in the conversion of the enzyme activity from dehydrogenase (type D) into oxidase (type O) and purification of the enzyme.

1. The ;xanthine oxidase' activity of rat liver supernatant, most of which behaves as an NAD(+)-dependent dehydrogenase (type D) can be rapidly converted into an oxidase (type O) by thiol reagents such as tetraethylthiuram disulphide, copper sulphate, 5,5'-dithiobis-(2-nitrobenzoic acid), N-ethylmaleimide and p-hydroxymercuribenzoate. Treatment with copper sulphate, if prolonged, leads to almost complete inactivation of the enzyme. The effect of these reagents is prevented by dithioerythritol, and in all cases but that of N-ethylmaleimide is reversed by the same thiol. 2. Dithioerythritol prevents and reverses the conversion of xanthine oxidase from type D into type O brought about by storage of rat liver supernatant at -20 degrees C, preincubation under anaerobic conditions, treatment with carbon or with diethyl ether, and reverses, but does not prevent, the conversion obtained by preincubation of the whole liver homogenate. 3. Conversion of the enzyme from type D into type O is effected by preincubation of rat liver supernatant with the sedimentable fraction from rat liver but not from chick or pigeon liver. The xanthine dehydrogenase activity of chick liver supernatant is not changed into an oxidase by preincubation with the sedimentable fraction from rat liver. 4. The enzyme activity of rat liver supernatant is converted from type D into type O during purification of the enzyme: the purified enzyme can be reconverted into type D by dithioerythritol. 5. The enzyme appears as an oxidase in the supernatant of rat heart, intestine, spleen, pancreas, lung and kidney. The enzyme of all organs but intestine can be converted into a dehydrogenase by dithioerythritol.

The regulation of xanthine oxidase. Inhibition by reduced nicotinamide-adenine dinucleotide of rat liver xanthine oxidase type D and of chick liver xanthine dehydrogenase.

1. Rat liver xanthine oxidase type D (NAD(+)-dependent) and chick liver xanthine oxidase are inhibited by NADH, which competes with NAD(+). 2. The addition of a NADH-reoxidizing system in the assay of these enzyme activities is proposed. 3. Rat liver xanthine oxidase type O (oxygen-dependent) is not affected by NADH.

The regulation of L-asparaginase activity in rats and mice. Effects of normal and malignant growth, of sex and of dietary changes.

1. The activity of l-asparaginase was very low in the liver of newborn rats and mice, and increased within a few days of birth. 2. In rats, but not in mice, the enzyme activity was higher in females than in males, was enhanced by administration of oestradiol, and was decreased by gonadectomy. 3. The enzyme activity decreased in mice starved or fed on a low-protein diet; in rats it was enhanced by starvation, by feeding them on a high-protein diet, or by administration of l-asparagine. 4. The asparaginase activity was decreased in regenerating liver, and was almost absent in the Morris hepatoma 5123.

Activity of nicotinamide-adenine dinucleotide pyrophosphorylase in liver nuclei. Effects of partial hepatectomy, hepatotoxins and dietary changes.

1. The activity of NAD pyrophosphorylase is lower in nuclei isolated from regenerating rat liver than in normal nuclei, and this is due to leakage of the enzyme from the nuclei during the isolation. 2. The NAD pyrophosphorylase activity is lower in liver nuclei from newborn rats, and from rats on a protein-free diet, but no leakage occurs in these cases. 3. Poisoning with alpha-amanitin brings about a transient enhancement of NAD pyrophosphorylase activity in mouse liver nuclei. 4. No changes of enzyme activity were observed after 72hr. starvation, administration of actinomycin D or infection with MHV3 virus.

Regulation of xanthine dehydrogenase in chick liver. Further experiments on the effects of inosine, actinomycin D and other factors.

1. It has been confirmed that the xanthine-dehydrogenase activity of chick liver is enhanced by starvation and by administration of inosine; the effects of these treatments are not additive. 2. Inosine has no effect when given to chicks depleted of the enzyme by feeding a low-protein diet. 3. Actinomycin D prevents the effect of inosine, but itself enhances the activity of xanthine dehydrogenase. 4. The xanthine-dehydrogenase activity is unchanged after addition of orotic acid to the diet, and is stimulated by injection of inorganic iron.