The configuration and location of the ribosidic linkage in the prosthetic group of citrate lyase (Klebsiella aerogenes).

The structure of the prosthetic group of citrate lyase (Klebsiella aerogenes) was studied by nuclear magnetic resonance and mass spectrometry. The spectra at 360 MHz of the nucleoside moiety (2'-ribosyladenosine) show the absence of 2'-hydroxyl proton, thus confirming the 2' position as the site of attachment of the second ribose moiety to the dephospho-CoA. This glycosidic linkage is found to be alpha(1" leads to 2') and is identical to that of poly(ADP-ribose). Studies of permethylation products by mass spectrometry support the above conclusion regarding the location of the ribosidic linkage.     

Application of jackknife procedures to inter-experiment comparisons of parameter estimates for the Michaelis-Menten equation.

The jackknife procedure is introduced as a means of making comparisons among Michaelis-Menten parameter estimates for six different experimental conditions. In addition to providing a solution to the general inter-experimental comparison problem, the jackknife procedure will provide valid parameter estimates even when some of the assumptions usually required for statistical analysis are violated, e.g., the random errors are not normally distributed and the variances are not homogeneous. Other recent variations of the jackknife have also been introduced and briefly investigated: (i) the linear jackknife, which is more efficient computationally, and (ii) the weighted jackknife, which reduces the influence of design points (substrate concentrations) that have an excessive influence on the precision of parameter estimates.     

Isolation of an aggregation inhibitory factor from non-adhesive mouse teratoma cells

An aggregation inhibitory factor (AIF) has been extracted from mouse ascites teratoma cells (that do not aggregate in culture) that retards adhesion of cultured teratoma cells of the same cell line (that do aggregate). Preliminary characterization of AIF on polyacrylamide gels suggests that AIF is a protein composed of four subunits. Extraction of AIF from ascites teratoma cells was accomplished without significant loss of viability by a technique involving the application of an electric field to large numbers of whole cells suspended in a hypertonic electrode buffer. In tests of adhesion, AIF consistently and immediately inhibited aggregation of cultured teratoma cells after 5, 10, 15, and 30 min of incubation. Furthermore, a reduced concentration of AIF resulted in a corresponding decrease in inhibition, suggesting a concentration-dependent action. AIF may help explain how cultured teratoma cells adhere, whereas ascites teratoma cells of the same subline do not adhere.     

Behavioural displays to gustatory stimuli in newborn rabbit pups

Motor displays in the face and head regions of 33 neonate rabbits(less than 24 hrs post partum) in response to taste stimulationwere examined. A droplet of taste solution was placed mediallyon the pup's lips and the ensuing behavioral repertoire wastallied over a 60 sec period in a double blind situation. Tastantsincluded 2 concentrations each of sucrose, saccharin, citricacid and quinine. Distilled water was used as a stimulant andfor intertrial rinses. Response characteristics to the varioustaste stimuli were differentiable, specific and reproduciblewithin and across animals. Certain response features were moreoften associated with one stimulus than with another. Quinineoften produced mouth opening (gaping) and head movements, whereassucrose was associated with a quiet animal licking and makingcharacteristic mouth movements. Sour reactions often resembledthose to sweet, but other features helped distinguish thoseresponses. Reactions proved to be concentration-dependent anddifferent from those to water. Quality and hedonic value wereusually accurately judged and corresponded to adult preferencebehaviors. It was inferred that rabbits at this early age arealready equipped with a functioning taste system up to the brainstemlevel. Cross-species comparisons of stereotyped reactions werediscussed.     

NAD hydrolysis: Chemical and enzymatic mechanisms

The pyridine nucleotide have important non-redox activities as cellular effectors and metabolic regulators [1–3]. The enzyme-catalyzed cleavage of the nicotinamide-ribosyl bond of NAD⁺ and the attendant delivery of the ADPRibosyl moiety to acceptors is central to these many diverse biological activities. Included are the medically important NAD-dependent toxins associated with cholera, diphtheria, pertussis, and related disease [4]; the reversible ADPRibosylation-mediated biological regulatory systems [5,6]; the synthesis of poly (ADPRibose) in response to DNA damage or cellular, division [7]; and the synthesis of cyclic ADPRibose as part of an independent, calcium-mediated regulatory system[8]. As will be presented in this chapter, all evidence points to both the chemical and enzyme-catalyzed cleavage of the nicotinamide-ribosyl bond being dissociative in character via an oxocarbenium intermediate.     

Diphtheria toxin. Site and configuration of ADP-ribosylation of diphthamide in elongation factor 2

Diphtheria toxin inactivates protein synthesis elongation factor 2 by catalyzing the ADP-ribosylation of a novel derivative of histidine, diphthamide, in the protein (Van Ness, B. G., Howard, J. B., and Bodley, J. W. (1980) J. Biol. Chem. 255, 10710-10716). In this report, we describe experiments involving nuclear Overhauser enhancement NMR spectroscopy which were undertaken to elucidate the site of ADP-ribosylation of diphthamide and the configuration of the glycosidic bond formed by the toxin. The essential result of these experiments is that, in ribosyl-diphthamide obtained by enzymatic digestion of ADP-ribosyl-elongation factor-2, the H-5 imidazole proton is near the R-4 proton of ribose. This result and others are consistent with the interpretation that diphtheria toxin covalently attaches ADP-ribose to the imidazole N-1 of diphthamide via an alpha-glycosidic linkage.     

A predominantly indigenous paternal heritage for the Austronesian-speaking peoples of insular Southeast Asia and Oceania

Modern humans reached Southeast Asia and Oceania in one of the first dispersals out of Africa. The resulting temporal overlap of modern and archaic humans-and the apparent morphological continuity between them-has led to claims of gene flow between Homo sapiens and H. erectus. Much more recently, an agricultural technology from mainland Asia spread into the region, possibly in association with Austronesian languages. Using detailed genealogical study of Y chromosome variation, we show that the majority of current Austronesian speakers trace their paternal heritage to Pleistocene settlers in the region, as opposed to more-recent agricultural immigrants. A fraction of the paternal heritage, however, appears to be associated with more-recent immigrants from northern populations. We also show that the northern Neolithic component is very unevenly dispersed through the region, with a higher contribution in Southeast Asia and a nearly complete absence in Melanesia. Contrary to claims of gene flow (under regional continuity) between H. erectus and H. sapiens, we found no ancestral Y chromosome lineages in a set of 1,209 samples. The finding excludes the possibility that early hominids contributed significantly to the paternal heritage of the region.