Regulation of polyamine biosynthesis by antizyme and some recent developments relating the induction of polyamine biosynthesis to cell growth

This review considers the role of antizyme, of amino acids and of protein synthesis in the regulation of polyamine biosynthesis.The ornithine decarboxylase of eukaryotic ceils and ofEscherichia coli coli can be non-competitively inhibited by proteins, termed antizymes, which are induced by di-and poly- amines. Some antizymes have been purified to homogeneity and have been shown to be structurally unique to the cell of origin. Yet, the E. c o l i antizyme and the rat liver antizyme cross react and inhibit each other's biosynthetic decarboxylases. These results indicate that aspects of the control of polyamine biosynthesis have been highly conserved throughout evolution.Evidence for the physiological role of the antizyme in mammalian cells rests upon its identification in normal uninduced cells, upon the inverse relationship that exists between antizyme and ornithine decarboxylase as well as upon the existence of the complex of ornithine decarboxylase and antizyme in vivo. Furthermore, the antizyme has been shown to be highly specific; its Keq for ornithine decarboxylase is 1.4 x 1011 M-1. In addition, mammalian ceils contain an anti-antizyme, a protein that specifically binds to the antizyme of an ornithine decarboxylase-antizyme complex and liberates free ornithine decarboxylase from the complex. In B. coli , in which polyamine biosynthesis is mediated both by ornithine decarboxylase and by arginine decarboxylase, three proteins (one acidic and two basic) have been purified, each of which inhibits both these enzymes. They do not inhibit the biodegradative ornithine and arginine decarboxylases nor lysine decarboxylase. The two basic inhibitors have been shown to correspond to the ribosomal proteins S₂₀/L₂₆ and L₃₄, respectively. The relationship of the acidic antizyme to other known B. coli proteins remains to be determined.     

Characterization, Localization, and Biosynthesis of an Interstitial Retinol-Binding Glycoprotein in the Human Eye

Abstract: Human eyes contain an M_r 135K retinol-binding protein that is analogous to interstitial retinol-binding protein (IRBP) in the subretinal space of bovine eyes. It is a glycoprotein, because it binds ¹²⁵I-concanavalin A, ¹²⁵I-wheat germ agglutinin and ¹²⁵I- Lens culinaris hemagglutinin. It does not bind Ricinus communis agglutinin I. After desialation, it binds Ricinus communis agglutinin I, but loses its capacity to bind wheat germ agglutinin. These observations, coupled with the known specificities of these lectins, suggest that at least one of the oligosaccharide chains is a sialated, biantennary complex type containing fucose. Both by direct analysis of dissected ocular tissues and by immunocytochemistry it was shown that human interstitial retinol binding protein is an extracellular protein that is confined predominantly to the subretinal space. Monkey retinas incubated in vitro in medium containing [³H]leucine were shown to synthesize and secrete this protein into the medium, a conclusion that was confirmed by immunoprecipitation with an immunoglobulin fraction prepared from rabbit antibovine IRBP serum. Virtually no other labeled proteins were detectable in the medium. It is concluded that interstitial retinol-binding protein meets many of the requirements for a putative transport protein implicated in the transfer of retinol between the pigment epithelium and retina during the visual cycle, and that the neural retina may play an important role in regulating its amount in the subretinal space.     

An extracellular retinol-binding glycoprotein in the eyes of mutant rats with retinal dystrophy: development, localization, and biosynthesis

Interstitial retinol-binding protein (IRBP) is a soluble glycoprotein in the interphotoreceptor matrix of bovine, human, monkey, and rat eyes. It may transport retinol between the retinal pigment epithelium and the neural retina. In light-reared Royal College of Surgeons (RCS) and RCS retinal dystrophy gene (rdy)+ rats, the amount of IRBP in the interphotoreceptor matrix increased in corresponding proportion to the amount of total rhodopsin through postnatal day 22 (P22). In the RCS-rdy+ rats, the amount increased slightly after P23. However, in the RCS rats there was a rapid fall in the quantity of IRBP as the photoreceptors degenerated between P23 and P29. No IRBP was detected by immunocytochemistry in rats at P28. The amount of rhodopsin fell more slowly. Although retinas from young RCS and RCS-rdy+ rats were able to synthesize and secrete IRBP, this ability was lost in retinas from older RCS rats (P51, P88) but not their congenic controls. The photoreceptor cells have degenerated at these ages in the RCS animals, and may therefore be the retinal cells responsible for IRBP synthesis. The putative function of IRBP in the extracellular transport of retinoids during the visual cycle is consistent with a defect in retinol transport in the RCS rat reported by others.     

Effects of Polyamines on the Uptake of Neurotransmitters by Rat Brain Synaptosomes

Abstract: The influence of putrescine, spermidine, spermine, and some aliphatic α,ω-diamines on the uptake of neurotransmitters by rat forebrain synaptosomes was investigated. Choline uptake was most effectively inhibited by spermine (IC₅₀= 0.22 m M ), less so by spermidine (IC₅₀= 4.0 m M ), but not by putrescine (IC₅₀ > 100 m M ). At 10 m M, 1,3-diaminopropane, cadaverine, and 1,8-diaminooctane all inhibited choline uptake by 50% or more. Spermine and spermidine inhibited the uptake of dopamine with IC₅₀ values of 2.7 and 2.2 m M , respectively. Putrescine was only slightly inhibitory (IC₅₀= 17.3 m M ) and the other diamines were inactive. The uptake of γ-aminobutyrate (GABA) was only slightly inhibited (15–40%) by the polyamines at 10 m M . With the exception of inhibition of glycine uptake by 1,8-diaminooctane (60%) and of glutamate uptake by cadaverine (35%) none of the polyamines, tested at 10 m M , affected the uptake of adenosine, glutamate, and glycine significantly. A possible modulatory role for polyamines in synaptic transmission through interaction by negatively charged groups of the synaptic membrane with the polycationic compounds is discussed.     

Proteolytic degradation of HDL1 on the fat cell surface is nutritionally regulated

The importance of plasma HDL apolipoprotein concentration as a predictor of atherosclerotic risk is well recognized, yet the processes of HDL modification and degradation in various cells are not clearly understood. We examined the characteristics of HDL1 apolipoprotein degradation and cellular uptake by rat adipocytes and determined the effects of fasting on these processes. Epididymal and perirenal adipocytes were isolated from male Wistar rats (310 +/- 4 g) fed ad libidum and incubated with 5 micrograms of rat 125I-labeled HDL1 (d: 1.07-1.10 g/mL) mL-1 for 2 h at 37 degrees C. Cellular uptake of HDL1 was calculated as the trichloroacetic acid precipitable radioactivity associated with adipocytes following incubation. Intracellular and medium degradation of HDL1 were determined as trichloroacetic acid soluble 125I counts associated with cells and measured in the postincubation medium, respectively. Fifty to sixty percent of cellular uptake and degradation of HDL1 was inhibited by the addition of 25-fold excess unlabeled HDL. HDL1 degradation measured in the medium was 10- to 12-fold greater than cellular uptake of HDL1 apolipoproteins. Intracellular degradation of HDL1 was negligible. The presence of EDTA in the incubation medium reduced HDL1 degradation measured in the medium, but enhanced HDL1 cellular uptake. Conditioned medium separated from cells after 2 h of incubation at 37 degrees C in the absence of HDL and subsequently incubated with 125I-labeled HDL1 for an additional 2 h at 37 degrees C, degraded less than 5% of HDL compared with degradation in the presence of cells. These results suggest that rat adipocytes degrade, or modify, HDL1 particles, possibly by interactions with cell surface proteases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Liver alcohol and aldehyde dehydrogenase isozymes in a Chinese population in Hong Kong

The distribution of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) isozymes in the livers of a Chinese population in Hong Kong was examined. Among the 90 livers examined, 7 were typical ADH phenotype consisting the normal beta 1-type isozymes and 83 were atypical phenotype consisting the beta 2-type isozymes. Livers of 48 subjects were of deficient type in ALDH containing ALDH-II alone and 42 were of normal type with both ALDH-I and ALDH-II. When the combination of ADH and ALDH isozymes is considered, the Chinese population in Hong Kong falls into 4 subgroups. For each group, the rates of ethanol and acetaldehyde clearance have a distinct and characteristic potential which is directly related to its particular combination of isozymes.     

Location and characterization of two functions on RP1 that inhibit the fertility of the IncW plasmid R388

Two fertility-inhibition functions which reduce R388 (IncW) transfer were detected on RP1 (60 kb, IncP). The respective genes, fiwA and fiwB, were mapped by transposon insertion mutagenesis to the regions between coordinates 32.8 to 31.7 kb (fiwA), and 59.8 to 0.8 kb (fiwB). The fiwA function occurs in a non-essential region of RP1 whereas fiwB is straddled by essential plasmid-maintenance and host-range determinants and apparently coincides (or overlaps) with the gene for tellurite-resistance.