A model for cleavage ofO-glycosidic bonds in glycoproteins

The present work investigated the possibility of cleavage of -linkages between mannose or galactose and serine/threonine residues by -mannosidase and -galactosidase. The study was carried out initially with model synthetic compounds imitating theO-glycosidic bond in glycoproteins, and further with glucoamylase. It was shown that -mannosidase and -galactosidase can hydrolyse these linkages after proteolytic digestion of glucosamylase.     

PATTERNS OF PLANT ONTOGENY THAT MAY INFLUENCE GENOMIC STASIS

It is an axiom in biology that genes control the ontogeny and ultimately the final form of an organism. In plants a given morphological form can often arise through more than one ontogenetic pattern of cell divisions. Different ontogenetic patterns have different properties with regard to the final age in cell divisions of the initials in the meristems for a given morphological form. If mutation per genome per cell division is an important biological metric, then since the age of a cell in cell divisions is a function of ontogeny, the cellular ontogeny will influence the degree of mutation-loading in meristematic initials. Thus, ontogeny and form may affect the genes (by promoting or lessening genomic stasis) as well as, of course, being determined by the genes. This paper explores mathematically the relationship between different patterns of cell division and mutation-loading.     

Structural and immunochemical studies on the lipopolysaccharide of the ‘T-antigen’-containing mutant Proteus mirabilis R14/1959

Abstract In DOC-PAGE, lipopolysaccharide (LPS) of Proteus mirabilis R14/1959 (Rb-type) mutant showed a ladder-like migration pattern indicating the presence of a high molecular weight polysaccharide chain. The isolated polysaccharide, called T-antigen because of similarity with the T1 chain of Salmonella friedenau LPS, contained d -glucose, d -galacturonic acid ( d -GalA), and d -GlcNAc in molar ratios 2:1:1 and was structurally different from the O-antigen of the parental S-strain P. mirabilis S1959 but identical to the O-antigen of another S-strain Proteus penneri 42. The importance of a d -GalA( l -Lys)-containing epitope, most likely present in the core region of LPS, and of GalA present in the T-antigen chain in manifesting the serological specificity of P. mirabilis R14/1959 were revealed using rabbit polyclonal homologous and heterologous R- and O-specific antisera and the appropriate antigens, including synthetic antigens which represent partial structures of various Proteus LPS.     

Intercontinental spread of promiscuous mercury-resistance transposons in environmental bacteria

We demonstrate that horizontal spread of mer operons similar to worldwide spread of antibiotic-resistance genes in medically important bacteria occurred in bacteria found in ores, soils and waters. The spread was mediated by different transposons and plasmids. Some of the spreading transposons were damaged in different ways but this did not prevent their further spread. Certain transposons are mosaics composed of segments belonging to distinct sequence types. These mosaics arose as a result of homologous and site-specific recombination. Our data suggest that the mercury-resistance operons of Gram-negative environmental bacteria can be considered as a worldwide population composed of a relatively small number of distinct recombining clones shared, at least partially, by environmental and clinical bacteria.     

Domain structure and interactions of recombinant urokinase-type plasminogen activator.

Urokinase-type plasminogen activator (uPA) is a mosaic glycoprotein composed of an epidermal growth factor-like (EGF), a kringle and a serine protease (SP) module. It exists in single and two-chain forms designated HMW pro-uPA and HMW uPA, respectively. A low molecular weight form, LMW uPA, lacks the EGF and kringle modules and is composed of the SP module alone. Recombinant-expressed proteins representing both HMW forms exhibit four reversible unfolding transitions that are resolved by deconvolution of melting curves obtained by differential scanning calorimetry at pH 4.5; no differences in the melting properties of the single and two-chain forms were found. The proteolytic fragment Ser1-Lys135 (EGF-kringle) exhibits two transitions, while the isolated EGF and kringle modules each exhibit a single two-state transition. Thus, both of these modules retain an independently folded compact structure when isolated. The isolated SP module (LMW uPA) exhibits two closely spaced transitions at low pH indicating the melting of two domains of similar stability. Fluorescence-detected melting curves of LMW uPA reveal increasing cooperativity with increasing pH, suggesting an increase in the interaction between the two SP domains. Treatment of both HMW and LMW uPA with the tripeptide inhibitor Glu-Gly-Arg-chloromethylketone dramatically increased the stability of both domains of the SP module which now melt together in a single two-state transition, even at low pH, with no effect on the EGF and kringle modules. From these data one concludes that UK consists of four independently folded domains. Two are formed by the EGF and kringle modules which do not interact with each other or with the SP module. The SP module contains two domains that are independent at low pH but exhibit a tendency to merge into a single cooperative unit at neutral pH or after treatment with the tripeptide inhibitor.     

Genetic control and expression of the major ejaculatory bulb protein (PEB-me) inDrosophila melanogaster

PEB-me is a predominant protein of matureDrosophila melanogaster ejaculatory bulbs. It is resolved into four or five closely spaced subfractions (apparent molecular weight 35–39 kD) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Four electrophoretic variants of PEB-me differing in apparent molecular weight by 200–800 daltons were found. These appear to be controlled by four alleles of a gene (peb) located by recombination and deletion mapping to the 60F1-2 region of chromosome 2. A minor ejaculatory bulb protein of ca. 80 kD (hPEB) was found to be immunochemically related to PEB and possibly encoded bypeb. PEB is not detected by immunoblotting techniques in virgin females, in male tissues other than the ejaculatory bulb, or during developmental stages preceding the formation of this organ. The results of transplantations of genital imaginal discs and of immature ejaculatory bulbs between two strains having different PEB alleles suggest that the ejaculatory bulb is the site of PEB synthesis. In flies mutant fortra, tra-2, dsx, orix, tissue specificity of PEB localization is retained and the protein is found whenever the ejaculatory bulb is formed, regardless of the chromosomal sex of the fly. The protein is transferred into the female genital duct during mating, where it can be detected for up to 12 hr. Possible functions of PEB inDrosophila reproduction are discussed.     

Effects of retinoic acid on protein synthesis in cultured melanoma cells

Retinoic acid reduces the growth rate of mouse S91 melanoma cells in culture and increases the proportion of cells in the G₁ phase of the cell cycle. Because of the integral role protein synthesis has been shown to play in growth control we studied the effect of retinoic acid on the protein synthesis machinery with a cell-free system developed from the melanoma cells. This system was capable of translating endogenous mRNA, exogenous globin mRNA, and the synthetic template poly(U). Of the above activities of the protein synthesis system only the translation of endogenous mRNA was reduced significantly in the cell-free system prepared from retinoic acid-treated cells. Analyses of the amount and function of RNA revealed that treatment with retinoic acid leads to reductions in total RNA content, in the proportion of ribosomes in polysomes, in the amount of poly(A)RNA, and in the amount of polysome-associated mRNA. All these effects of retinoic acid contribute to the decrease in protein synthesis activity of treated cells. Two-dimensional electrophoresis anlaysis of L-[³⁵S]methionine-labeled proteins produced by untreated and treated cells revealed only a few quantitative differences. We suggest that retinoic acid-induced suppression of protein synthesis activity may be the cause for growth inhibition.     

Predation by the desert pupfish,Cyprinodon macularius onCulex mosquitoes and benthic chironomid midges

Predation ofCulex mosquitoes and chironomid midges was demonstrated byCyprinodon macularius Baird & Girard in two types of shallow ponds. In large ponds (5.5×2.6 m) with fish, all mosquito breeding ceased 4 weeks after introduction ofC. macularius. A significant, density-dependent reduction of several chironomid biotypes was sustained, although an increase was evident for other chironomid biotypes. Fish biomass increased 2.43 fold in 76 days in m² ponds and 23.22 fold in 70 days in larger ponds. Behavioral studies showedC. macularius capable of feeding effectively on mosquitoes in floating algal mats. The desert pupfish deserves serious attention in the biological-integrated control of medically important aquatic arthropods, and may possess attributes making it a preferred, ecologically adapted substitute forGambusia affinis (Baird & Girard) in certain habitats.     

Reduction in number of sarcolemmal KATP channels slows cardiac action potential duration shortening under hypoxia

The cardiovascular system operates under demands ranging from conditions of rest to extreme stress. One mechanism of cardiac stress tolerance is action potential duration shortening driven by ATP-sensitive potassium (K_ATP) channels. K_ATP channel expression has a significant physiologic impact on action potential duration shortening and myocardial energy consumption in response to physiologic heart rate acceleration. However, the effect of reduced channel expression on action potential duration shortening in response to severe metabolic stress is yet to be established. Here, transgenic mice with myocardium-specific expression of a dominant negative K_ATP channel subunit were compared with littermate controls. Evaluation of K_ATP channel whole cell current and channel number/patch was assessed by patch clamp in isolated ventricular cardiomyocytes. Monophasic action potentials were monitored in retrogradely perfused, isolated hearts during the transition to hypoxic perfusate. An 80–85% reduction in cardiac K_ATP channel current density results in a similar magnitude, but significantly slower rate, of shortening of the ventricular action potential duration in response to severe hypoxia, despite no significant difference in coronary flow. Therefore, the number of functional cardiac sarcolemmal K_ATP channels is a critical determinant of the rate of adaptation of myocardial membrane excitability, with implications for optimization of cardiac energy consumption and consequent cardioprotection under conditions of severe metabolic stress.