Quantification of two viruses in technical preparations of Orgyia pseudotsugata baculovirus by means of buoyant density centrifugation of viral deoxyribonucleic acid.

A reliable method was developed for the quantitative determination of two nuclear polyhcdrosis viruses present in commercially prepared viral insecticides used against Orgyia pseudotsugata. Deoxyribonucleic acids, from nuclear polyhedrosis bundle virus and nuclear polyhedrosis single-rod virus, were separated on CsCl gradients according to their respective buoyant densities, 1.715 and 1.704 g/ml. The proportions of the two viruses were quantified by measuring the relative absorbance at 254 nm of their deoxyribonucleic acid peaks.     

Characterization of ribonucleolytic activity of angiogenin towards tRNA

Yeast tRNA is a convenient substrate for the assay of the ribonucleolytic activity of human angiogenin. The optimal pH, [NaCl], and temperature for tRNA cleavage by angiogenin are approximately 6.8, 15-30 mM, and approximately 55 degrees C, respectively, as compared with approximately 8.0, 100-200 mM, and approximately 65 degrees C, respectively, for RNase A. Polyanions and metals both inhibit angiogenin and RNase A but to different extents.     

Cysteine control over glutathione homeostasis in Chinese hamster fibroblasts overexpressing a gamma-glutamylcysteine synthetase activity.

Gamma-glutamylcysteine synthetase (GCS) catalyses the first step of glutathione (GSH) biosynthesis and is considered to be the rate-limiting step of this pathway. In several experimental systems, GCS overexpression has been associated with GSH pool expansion and drug resistance. In this report, we describe a mutant line of Chinese hamster fibroblasts that overexpress this activity by 4-5 times, due to the amplification of the gene encoding the catalytic subunit of GCS. These mutant cells contained a wild-type steady-state level of GSH and, after depletion, synthesized GSH at the same rate as wild-type cells because their rate of endogenous production of cysteine was limiting. An exogenous supply of cysteine expanded the pool of GSH in mutant cells by 80% but did not increase that of wild-type cells, and, in GSH-depleted cells, increased the rate of GSH biosynthesis by eight and 35-times in wild-type and mutant cells, respectively. These experiments indicated that GCS overexpression had no consequence on the metabolism of GSH, unless a supply of cysteine was provided. Mutant cells were not resistant to cisplatin or nitrogen mustard.     

Structural features of the brains of rats selected for their thresholds of neuromuscular excitability

As a result of selection of rats possessing a high threshold of neuro-muscular exitability in comparison with rats possessing a low threshold of neuro-muscular exitability, certain changes take place in the structures that are connected with the learning process: the visual cortex is wider, volumes of the pyramidal cells in the fields CA1 and CA3 of the hippocampus are increased, density of the glial elements in the fornix is essentially increased and that of neurons in the septal nucleus is decreased.     

Near-infrared spectroscopy for bioprocess monitoring and control.

This article describes the calibration of a spectroscopic scanning instrument for the measurement of selected contaminants in a complex biological process stream. Its use is for the monitoring of a process in which contaminants are to be removed selectively by flocculation from yeast cell homogenate. The main contaminants are cell debris, protein, and RNA. A low-cost instrument has been developed for sensitivity in the region of the NIR spectrum (from 1900 to 2500 nm) where preliminary work found NIR signatures from cell debris, protein, and RNA. Calibration models have been derived using a multivariate method for concentrations of these contaminants, such as would be found after the flocculation process. Two strategies were compared for calibrating the NIR instrument. In one case, samples were prepared by adding materials representative of the contaminants to clarified yeast homogenate so the contaminant levels were well known but outside the range of interest. In the other case, where samples were like those from the process stream after flocculation and floc removal, there was uncertainty of analysis of contaminant level, but the calibration was in the range of interest. Calibration using process stream samples gave results close to those derived from traditional assays. When the calibration models were used to predict the contaminant concentrations in previously unseen samples, the correlation coefficients between measurements and predictions were above 90% in all cases but one. The prediction errors were similar to the errors in the traditional assays.