Volume 87, Issue 1
January 1978, pages 1-79
pp 1-8 January 1978 Immunology
Leukaemia specific antigens have been isolated from the membranes of dinitrophenylated normal human leukocytes (104 molecules of l-fluoro, -2, 4-dinitrobenzene per cell). Affinity chromatography on antibody-sepharose column separated two macromolecular moieties with molecular weights of 21000 and 48000. The isolated antigens elicited immune response specific against human leukaemic cells. The use of oil-in-water emulsion with isolated antigens was essential during immunization to achieve appropriate hydrophylic-hydrophobic conformation similar to that seen on the native cell surfaces.
pp 9-23 January 1978 Microbiology and Cell Biology
Axenically grown trophozoites of Entamoeba histolytica, starch fed and toxin treated, when incubated in a minimal medium containing epinephrine and theophylline at 33° ± 1°C were transformed to a round form with a thick outer wall; in contrast, the untreated cells died. These round bodies or “precysts” hatched to the trophic form when transferred to fresh growth medium. Formation of round bodies occurred even in the absence of cysteine but they were not mature and readily disintegrated.
The starch treated cells possessed nearly twice the activity of amylase as present in the control cells. The activity of glycogen phosphorylase was comparable in the control and starch fed cells. Glycogen synthetase activity was not detected in the control or starch fed cells. Axenically grown cells did not accumulate DL (7-3H) epinephrine, but after feeding on starch the cells accumulated the amine readily which was found distributed almost equally between the particulate fraction and the particulate-free cytoplasm. The uptake of epinephrine was significantly inhibited by propranolol, a β-adrenergic blocker but not by phentolamine, an α-adrenergic blocker. The amine was bound to the protein fraction of the particulate material.
pp 25-29 January 1978 Microbiology and Cell Biology
By the isolation of mutants that were unable to grow on L-hydroxyproline or DL-valine, it has been possible to demonstrate the presence of two different types of D-amino acid oxidase activities inPseudomonas aeruginosa PAO. One was the D-amino acid dehydrogenase, probably involved in the oxidation of a number of D-amino acids such as D-alanine, D-phenylalanine and D-valine. The other was the inducible oxidase, specific to the oxidation of allohydroxy-D-proline formed from L-hydroxyproline during its oxidation. Thus, it has been possible to delink the involvement of the general D-amino acid dehydrogenase in the oxidative breakdown of allohydroxy-Dsproline.
pp 31-39 January 1978 Microbiology and Cell Biology
The effect of DL-7-azatryptophan, an analogue of tryptophan, has been studied on the heterocyst spacing pattern and the probability of proheterocyst regression inAnabaena doliolum. 7-azatryptophan suppressed growth and induced heterocyst differentiation in nitrogen-free medium. In ammonium (1 mM), nitrite (2 mM) and nitrate (2 mM) supplemented media, it caused proheterocyst regression with a frequency of 100%, 35% and 10% respectively. The role of azatryptophan in nitrogen metabolism has been discussed in relation to ammonia-uptake study.
pp 41-51 January 1978 Endocrinology
Initiation of follicular growth by specific hormonal stimuli in ovaries of immature rats and hamsters was studied by determining the rate of incorporation of3H-thymidine into ovarian DNAin vitro. Incorporation was considered as an index of DNA synthesis and cell multiplication.
A single injection of pregnant mare serum gonadotropin could thus maximally stimulate by 18 hr3H-thymidine incorporation into DNA of the ovary of immature hamsters. Neutralization of pregnant mare serum gonadotropin by an antiserum to ovine follicle stimulating hormone only during the initial 8–10 hr and not later could inhibit the increase in3H-thymidine incorporationin vitro observed at 18 hr, suggesting that the continued presence of gonadotropin stimulus was not necessary for this response. The other indices of follicular growth monitored such as ovarian weight, serum estradiol and uterine weight showed discernible increase at periods only after the above initial event.
A single injection of estrogen (diethyl stilbesterol or estradiol-l7β) could similarly cause 18 hr later, a stimulation in the rate of incorporation of3H-thymidine into DNAin vitro in ovaries of immature rats. The presence of endogenous gonadotropins, however, was obligatory for observing this response to estrogen. Evidence in support of the above was two-fold: (i) administration of antiserum to follicle stimulating hormone or luteinizing hormone along with estrogen completely inhibited the increase in3H-thymidine incorporation into ovarian DNAin vitro; (ii) a radioimmunological measurement revealed following estrogen treatment, the presence of a higher concentration of endogenous follicle stimulating hormone in the ovary. Finally, administration of varying doses of ovine follicle stimulating hormone along with a constant dose of estrogen to immature rats produced a dose-dependent increment in the incorporation of3H-thymidine into ovarian DNAin vitro. These observations suggested the potentiality of this system for developing a sensitive bioassay for follicle stimulating hormone.
pp 53-61 January 1978 Biophysics
The effect of the urea-class of protein denaturants on the structure of liquid water was studied. The method chosen was to monitor the microviscosity of the medium by estimating the reorientational correlation time, τ8 and proton hyperfine linewidth, WH of an inert stable organic free radical (2, 2, 6, 4-tetramethyl-piperid 4-one-l-oxyl) by measuring its electron spin resonance spectra in aqueous denaturant solutions. Urea, thiourea and guanidinium chloride were found to disrupt water structure efficiently and continuously, with the effect significant at low molarities. Dimethyl urea was found to be somewhat less efficient. The relation between the structure-breaking tendency of the denaturants and their ability to weaken hydrophobic interactions is rationalised.
pp 63-66 January 1978 Biochemistry
Saline extracts of several varieties ofTriticale had haemagglutinin activity against rabbit, rat and fowl erythrocytes. In contrast to the wheat germ lectin theTriticale lectin was inactive against human B, 0 blood group type erythrocytes and rather high concentrations of the lectin are needed to agglutinate human A blood group type erythrocytes. TheTriticale lectin was purified about 20-fold with a 10% recovery of activity from one of the varieties (DTS 138) by (NH4)2SO4 fractionation followed sequentially by chromatography on DEAE-cellulose and sulphopropyl-Sephadex. Approximately 4 μg of the purified lectin caused visible agglutination with trypsinised rabbit erythrocytes. Among a variety of sugars tested D-glucose, D-mannose and N-acetyl-D-glucosamine (2·5-7·5mM) caused inhibition of agglutination.
pp 67-79 January 1978 Biochemistry
Aspartate transcarbamylase (EC 2·1·3·2) purified from mung bean seedlings was used as a model to understand the mechanism of allosteric regulation. The enzyme exhibited homotropic interactions with carbamyl phosphate. Preincubation of the enzyme with aspartate abolished the sigmoidicity of the carbamyl phosphate saturation curve. UMP was the most potent inhibitor of the reaction and was noncompetitive with respect to aspartate. The sigmoidicity of carbamyl phosphate saturation curves increased with increase in UMP concentration. These results were analysed by an iterative least squares procedure. There was no change inVmax values with increase in the UMP concentration, although theK0·5 values (concentration of carbamyl phosphate required to reach half maximal velocity) increased. This implied that the effect of UMP was on the binding of carbamyl phosphate only and not on the catalytic function of the enzyme. The allosteric properties of the enzyme could be explained in terms ofK system of the symmetry model. The values of the allosteric constantsn, L andc calculated for mung bean enzyme, making use of the Monod equation accounted for all the observed properties. The enzyme appeared to be a tetramer (n=4) and in the absence of ligands was predominantly in theT form (Lo= 2·25). Carbamyl phosphate bound preferentially to theR form (c= 10−3), while UMP bound preferentially to theT form and hence these two ligands exhibited the typical heterotropic interactions as expected of antagonistic ligands.