Volume 20, Issue 5
December 1995, pages 573-706
pp 573-578 December 1995
The kinetics of interfacial proton transfer reaction is an important factor in proton transport across membranes. The following experimental system was designed in order to measure this kinetics. Sonicated liposomes having the protonophore SF6847 was suspended in Tris buffer. Application of a temperature jump (in ∼ 3 μs) caused a drop in the aqueous phase pH which was subsequently sensed by the membrane-bound SF6847. The kinetics of this interfacial proton transfer reaction was monitored on μs timescales. The estimated bimolecular rate constant of 2×1011 M−1 s#x2212;1 for this process show that there is no kinetic barrier for the transfer of protons from the aqueous phase to the membrane-water interface.
pp 579-590 December 1995
A large protein sequence database with over 31,000 sequences and 10 million residues has been analysed. The pair probabilities have been converted to entropies using Boltzmann’s law of statistical thermodynamics. A scoring weight corresponding to “mixing entropy” of the amino acid pairs has been developed from which the entropies of the protein sequences have been calculated. The entropy values of natural sequences are lower than their random counterparts of same length and similar amino acid composition. Based on the results it has been proposed that natural sequences are a special set of polypeptides with additional qualification of biological functionality that can be quantified using the entropy concept as worked out in this paper.
pp 591-611 December 1995
Conformational studies have been carried out on hydrogenbonded all-trans cyclic pentapeptide backbone. Application of a combination of grid search and energy minimization on this system has resulted in obtaining 23 minimum energy conformations, which are characterized by unique patterns of hydrogen bonding comprising of β- and γ-turns. A study of the minimum energy conformationsvis-a-vis non-planar deviation of the peptide units reveals that non-planarity is an inherent feature in many cases. A study on conformational clustering of minimum energy conformations shows that the minimum energy conformations fall into 6 distinct conformational families. Preliminary comparison with available X-ray structures of cyclic pentapeptide indicates that only some of the minimum energy conformations have formed crystal structures. The set of minimum energy conformations worked out in the present study can form a consolidated database of prototypes for hydrogen bonded backbone and be useful for modelling cyclic pentapeptides both synthetic and bioactive in nature.
pp 613-627 December 1995
Instability and polymorphism at several CAG/CTG trinucleotide repeat loci have been associated with human genetic disorders. In an attempt to identify novel sites that may be possible loci for expansion of CAG/CTG repeats, we searched all human sequences in the EMBL nucleotide sequence database for (CAG)5 and (CTG)5 repeats. We have identified 121 human DNA sequences of known and unknown functions that contain stretches of five or more CAG or CTG repeats. Many repeat stretches were interrupted by variant triplets, a significant number of which differ from the repeat triplet only by a single base, suggesting that these evolved from the parent triplet by point mutations. A large number of human transcription factor genes were found to contain CAG repeats within their coding sequences. Analysis of the EMBL transcription factors database showed that many transcription factor genes of other eukaryotes, including genes involved inDrosophila embryo development, possess these repeats. Interestingly, CAG repeats are absent from prokaryotic transcription factors. Different sequence entries for the human TATA box binding protein showed a polymorphism in the length of the CAG repeat in this gene, suggesting that loci other than those already known to be associated with genetic diseases may be possible sites for repeat instability related disorders. On the basis of our findings in this database analysis, we propose a role for CAG repeats as cisacting regulatory elements involved in fine-tuning gene expression.
pp 629-636 December 1995
Starch, total sugars, reducing sugars and protein contents and the specific activities of hydrolytic enzymes such as amylase, Phosphorylase, soluble acid invertase, wall-bound acid invertase, sucrose synthetase, acid and alkaline phosphatases and ribonuclease were determined in root forming, shoot forming and non-organ-forming callus cultures of tobacco. Organ-forming cultures not only showed higher amounts of the above metabolites but also higher enzyme activities compared to non-organ-forming cultures. The activities of these enzymes in relation to organogenesis is discussed.
pp 637-644 December 1995
When electrophoretic profiles of native proteins from vegetative mycelia ofPhytophthora palmivora, Phytophthora capsici and Phytophthora citrophthora causing black pod disease of cocoa in India were compared on a single Polyacrylamide gel, the isolates of same species were readily distinguished both qualitatively by visual similarity in banding patterns and quantitatively by calculating similarity coefficients. Similarity coefficients were generally much higher between isolates within a species than between isolates of different species. The dendrograms obtained after unweighted pair grouping with arithmetic averaging cluster analysis, revealed that all the isolates ofPhytophthora capsici were highly homogenous and formed a single cluster. The isolates ofPhytophthora citrophthora were resolved into two electrophoretic types which were clustered into two distinct sub groups.Phytophthora palmivora formed a separate group. Thus, the results reveal that polyacrylamide gel electrophoresis can be used successfully in distinguishing species and sub groups within a species ofPhytophthora encountered on cocoa.
pp 645-655 December 1995
A simple protoplast isolation protocol that was designed to recover totipotent plant protoplasts with relative ease has been described. The key elements of the protocol are, tissue digestion at slightly elevated temperatures and use of protoplast-releasing enzymes that are stable and efficient at higher temperatures. Besides enzymes, the protoplast isolation cocktail consisted of an osmoticum (mannitol or MgSO4), and a protectant (CaCl2 2H2O), all dissolved in distilled water. The protocol has ensured reproducibility, higher yields and is gentle on protoplasts as the protoplasts obtained were amenable to cell wall regeneration and cell division. Plant regeneration was demonstrated forNicotiana tabacum cv. Thompson from protoplasts isolated by this method. Wall regeneration and cell division were obtained in other species. The merits of the protocol are, simple and easy-to-handle procedure, non-requirement of preconditioning of donor plant and explants, incubation without agitation, satisfactory yields, culturability of the protoplasts isolated and applicability of the protocol to a large number of species including mucilage-containing plants.
pp 657-664 December 1995
Members of the genusPassiflora are reported to have evolved modifications which kill insects; they have however never been tested for carnivorous syndrome. The flowers ofPassiflora foetida consists of highly reticulate bracts which cover and grow along with the buds and fruits. Removal of bracts from developing bud and fruit resulted in higher predatory damage compared to those where the bracts were intact. These bracts also possess a large number of minute glands which ooze sticky secretion. A variety of tiny insects were found trapped by the secretion of the bracts. The secretion of these glands show high proteases and acid phosphatase activity, two common digestive enzymes found in traps of true carnivorous plants. A high quantity of aminoacids were released from freshly freeze killed ants when incubated in buffer extract of bracts-[14C] phenylalanine smeared on the glandular surface of bracts was recovered from ovules suggesting potential for absorption of aminoacids. These results suggest a novel role for bracts where primary function is to minimize predatory damage to developing flowers and fruits. The bracts serve as insect traps and also possess the mechanism to digest the trapped insects to obtain free aminoacids.
pp 665-673 December 1995
The estrogen agonistic and antagonistic properties of clomiphene citrate were investigated in the mice. Clomiphene citrate was tested at various doses of 0.1, 1.0, 10 and 100 μg for three consecutive days in immature and mature bilaterally ovariectomized mice. Clomiphene citrate showed uterotrophic activity in both immature and ovariectomized conditions. The lower doses of 0.1 and 1.0 μg were ineffective to show any uterotrophic stimulation. Clomiphene citrate at 10 μg dose produced 305.56% increase in uterine weight i.e., 27.70 ± 0.24 vs 6.83 ± 0.06 in immature and 182.27% i.e., 42.68 ± 1.12 vs 15.12 ± 0.57 in ovariectomized mice. Clomiphene citrate at 100 μg dose showed significant uterotrophic effect e.g., 435.57% i.e., 36.58 ±0.34 vs 6.83 ± 0.06 in immature and 586% i.e., 103.80 ± 0.60 in ovariectomized mice. When clomiphene citrate was administered in combination with 0.32 μg of estradiol 17-β it caused significant antagonistic effect (decrease in uterine weight) at 10 and 100 μg respectively. Clomiphene citrate at 10 μg dose produced 32% i.e., 28.93 ± 0.43 vs 38.04 ± 2.68 in immature and 35% i.e., 59.64±1.44 vs 83.34 ±0.25 in ovariectomized mice respectively. Histological observation clearly showed that clomiphene citrate at 10 and 100 μg doses did not cause any differential hypertrophy of the epithelial layer. Similar doses in combination with estradiol produced significant antagonistic effect on uterine weight and luminal epithelial cell height.
pp 675-689 December 1995
The testis of Japanese eel (Anguilla japonica) consists of type A and early type B spermatogonia together with inactive Leydig and Sertoli cells. A single injection of human chorionic gonadotropin induced marked changes in the morphology of the testis and in the serum androgen levels within a period of 72 h. Morphological changes include spermatogonial proliferation, activation of Leydig and Sertoli cells, organization of seminiferous lobules and formation of lobular lumen in the testis. Leydig cells were enlarged, exhibiting characteristics of steroid-producing cells. Sertoli cells become elongated, show signs of high cellular activity and remain in close contact with spermatogonia. The lobular organization was achieved much earlier than the progression of spermatogenesis to late type B spermatogonia. Even 6 h after hCG injection, a significant increase in plasma levels of 11-ketotestosterone was observed, followed by a further time dependent increase. Plasma testosterone levels were also increased after injection, but the increase was much less than that of 11-ketotestosterone.
pp 691-706 December 1995
Unlike the other penaeiodean shrimp, the ridge back shrimp, Sicyoniaingentis does not produce a spermatophore, but transfers sperm suspended in seminal plasm. This paper reports on the histomorphology and ultrastructure of the vas deferens with reference to its functional role in secreting the sperm bearing materials. The vas deferens is divisible into proximal secretory, mid storage and distal ejaculatory regions. The epithelial cells lining the proximal vas deferens are comprised of secretory and absorptive cell types. The loose sperm cells found in the lumen of this region are in an immature condition, and are agglutinated into a compact mass with signs of spermiogenesis in the mid vas deferens. The epithelial cells lining the mid vas deferens are short flattened cells. The distal vas deferens is ensheathed by muscular fibres. The inner epithelial cells are highly secretory and contain numerous microvilli at the luminal end. The sperm cord gets liquefied in this region facilitating the transfer of sperm in liquid form to the female during mating.