Unlikelihood that minimal phylogenies for a realistic biological study can be constructed in reasonable computational time

The problem of determining a phylogeny of maximum parsimony from a given set of protein sequences is defined. It is shown that this problem is what is called, in computer science, NP-complete. The implication of this result is that it is equivalent in difficulty to a host of other problems in combinatorial optimization which are notorious for their intractability. This implies that it is more fruitful to attempt to develop heuristic techniques (which do not guarantee maximum parsimony but which do run in reasonable computer time) than to try to develop exact algorithms for phylogeny construction     

Quantitative relationships between the measurable transport resistances of membrane carriers: theory and experiment

A theoretical analysis is made of the possible quantitative relationships between the transport resistances that characterise membrane carrier systems. It is shown that there exist only five possible patterns in which to rank the four transport resistances. Symbolising these as A, B, C and D, the five possible patterns are (i) A = B = C = D; (ii) A = B much greater than C, D; (iii) A = B much greater than C = D; (iv) A = B = 2C = 2D; (v) A = 2B = 2C much greater than D. A survey of the available experimental data shows that pattern (ii) is the most prevalent, pattern (v) is often found and pattern (iii) has been identified. None of the ten transport systems so far analysed experimentally failed to fit one of the predicted patterns.     

S-oxalylglutathione is a substrate for gamma-glutamyltransferase (GGT). Implications for the role of GGT in cell proliferation

With glycylglycine or water as acceptor, bovine kidney gamma-glutamyltransferase catalyzes reactions of the known mammalian metabolite, S-oxalylglutathione, at rates comparable to those of L-gamma-glutamyl-p-nitroanilide, a known good substrate. N-Oxalyl-cysteinylglycine is the eventual product of the former reaction. Since oxalyl thiolesters are implicated as important cell proliferation inhibitors, it is proposed that this reaction plays a major role in controlling cell proliferation.     

The phosphorylation of adrenal proteins in response to adrenocorticotropic hormone

The phosphorylation of rat adrenal protein components in response to adrenocorticotropin has been studied in adrenal quarters, isolated cells, and in vivo. In adrenal quarters, adrenocorticotropic hormone (ACTH)-stimulated phosphorylation or dephosphorylation of proteins was not affected by the presence of protein synthesis inhibitors despite a total inhibition of steroidogenesis. (The term dephosphorylation refers to an apparent decrease in the labeling of a particular protein with 32P at various times after the addition of ACTH. This may be due to enzymatic removal of phosphate or protein degradation or complexation of this protein with another cellular component.) Studies with isolated cell preparations identified several proteins that are phosphorylated or dephosphorylated in response to hormone. These changes in phosphorylation were also observed in adrenal quarters and correlated well with ACTH-stimulated steroidogenesis as determined by temporal analysis and dose-response studies of corticosterone production. In vivo injection of male hypophysectomized rats with [32P]phosphate and ACTH demonstrated changes in the labeling of six adrenal proteins. Many of the proteins phosphorylated in vivo were also demonstrated to be phosphorylated in both in vitro systems. Finally, the injection of a physiological dose of ACTH appeared to selectively activate the type I cAMP-dependent protein kinase within the microsomal fraction as determined by the binding of a photoaffinity-labeled reagent. These results suggest that alterations in phosphorylation of adrenal proteins in response to ACTH is proximal to or independent of the obligatory role of protein synthesis in acute steroidogenesis.     

Absorption of light in photoreceptors: Effect of waveguiding property

The effect of waveguiding property (i.e., the intensity distribution) of the photoreceptor on the number of photons absorbed in a photoreceptor has been studied. It has been found that the effect is significant only for large values of the exposure and the maximum effect is less than 11% in the case of human rod photoreceptor. In the analysis, the funnelling effect, which follows from the coupling between the interior and exterior fields, has not been considered.Work partially supported by the Department of Science and Technology (India)B. D. Gupta is associated with the School of Bioscience Studies     

Widespread occurrence of AP in amyloidotic tissues. An immunohistochemical observation

Plasma (P)-component of amyloid (AP or SAP), while not an integral part of the amyloid fibril, has been considered to be intimately associated with virtually every different type of amyloid. In the present study, we evaluated the distribution of AP in the organs frequently involved in two forms of human systemic amyloidosis (AA and AF) and in mouse AA amyloidosis, by use of immunohistochemistry with anti-AP. Although the amyloid deposits generally showed moderate reactions with anti-AP, they were not always clearly distinguished from the surrounding non-amyloid tissue elements which often stained as well. The basement membrane often showed even stronger reaction to anti-AP than the adjacent amyloid deposits, and liver sections demonstrated such a high overall reaction to anti-AP that the anti-AP reaction on the amyloid deposits was often obscurred. The present results suggest that the binding between AP and the amyloid fibril may not be monospecific, that AP by this technique occurs rather widely throughout the body, and therefore that anti-AP may not be considered as specific a marker for amyloid deposits in immunohistochemical and perhaps other studies as well.     

Photoreaction of bacteriorhodopsin at high pH: origins of the slow decay component of M.

The absorption spectrum of light-adapted purple membrane in 3 M KCl is dependent on temperature even in the room temperature region. Temperature-induced difference spectra at various pH values suggested that the trans isomer of bacteriorhodopsin, bR570, is in thermal and/or photodynamic equilibrium with several different conformers. The major second conformer occurring at neutral pH had the same spectroscopic properties as the 13-cis isomer, and its content at 35 degrees C was estimated to be more than 20%. Heterogeneity in the protein conformation became more significant above pH8, where temperature-induced difference spectra exhibited a negative peak at 580 nm and a positive peak at 296 nm. This absorption change is very similar to that observed upon the formation of the N intermediate, suggesting that an N-like conformer occurs at high pH and temperature. A significant temperature dependence was also seen in the M decay kinetics at high pH, which were described by two decay components; i.e., the fast decaying M (Mf) was predominant at low temperature, but the amplitude of the slow component (M(s)) increased with increasing temperature. It is suggested that M(s) is generated upon excitation of the N-like conformer, in which the residue (Asp-96) usually acting as a proton donor to the Schiff base is deprotonated. The N-like conformer could be N itself, because M(s) was enhanced when N was accumulated by background light. A strong correlation between the amplitude of M(s) and the concentration of N was also revealed by the accumulation kinetics of Mf, M(s), and N after the onset of continuous actinic light.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of temperature on growth of guanidine-resistant mutants of poliovirus

Guanidine-resistant (gr) mutants of poliovirus were previously categorized into four groups by electrophoretic properties and peptide maps of nonstructural virus protein 2C. Growth of mutants in the presence of guanidine depends upon temperature of incubation. The four groups of gr variants respond differently to temperature when guanidine is included in the culture medium. The data suggest clustering of gr mutations at several sites in the guanidine locus.