The Catabolism of Plasma Albumin in the Rabbit : Its rate and regulation

From I¹³¹-albumin studies and previously defined mathematical formulations, rates of breakdown were estimated for native plasma albumin in rabbits. These rates of catabolism per unit weight of animal were remarkably constant and were independent of variations in the steady state values of albumin concentration in the plasma. These results imply that, at least between animals, the breakdown of plasma albumin follows a kinetic process of approximately zero order. It seems plausible that the process operates similarly in individual animals, and hence that albumin is maintained at normal steady state levels in the healthy animal primarily by means of a regulated rate of synthesis.     

Kinetics and mechanism of catalysis by proteolytic enzymes: The kinetics of hydrolysis of derivatives of l-lysine and S-(beta-aminoethyl)-l-cysteine(thialysine)by bovine trypsin

1. Several esters of the α-N-toluene-p-sulphonyl and N-benzoyl derivatives of l-lysine and S-(β-aminoethyl)-l-cysteine have been synthesized. 2. The kinetics of hydrolysis of the esters by bovine trypsin have been compared. Values of k₀ are similar for corresponding derivatives of the isosteric amino acids and deacylation of an acyl-enzyme appears to be rate-determining in each case. There are, however, some quantitative kinetic differences between the various series of substrates.     

Sporulation of Clostridium botulinum Type E in Different Culture Media

Twenty-seven strains of Clostridium botulinum type E were inoculated into six culture media and examined for production of spores. Thirty-six similar media were then inoculated with each of five strains. Strains varied greatly in their ability to form spores in a given medium. Spore formation varied markedly with casein digests and peptones of different manufacturers. Some differences were broadly indicated between strains from the Pacific and from Scandinavia.     

Antiplasmodial activity of Artemisia annua plant cell cultures

Extracts of Artemisia annua cultures have been assessed for in vitro activity against the malarial parasite Plasmodium falciparum. Callus and suspension cells and medium were analysed and examined for their activity at different stages of growth and development. Time-course experiments were carried out to investigate the influence of various basal media, plant growth regulators and light on both growth and possible artemisinin production. Two active fractions were obtained but artemisinin was not detected.     

Expression of insulin-like growth factor-I and its receptor by SV40-transformed rat granulosa cells

Cellular proliferation is a dominant aspect of ovarian follicular development in the rat, and insulin-like growth factor I (IGF-I) has been proposed as a mediator of cellular growth and differentiation in the ovary. An SV40-transformed rat granulosa cell line (RGA-41S) has been established as a model for studies on dividing cells of granulosa origin. Granulosa cells from the ovaries of immature diethylstilbestrol-treated rats were infected with the tsA255 mutant of SV40, followed by cloning in serum-free medium to select transformed cell lines which were serum independent. At the permissive temperature (33 C), RGA-41S cells exhibited a transformed phenotype and rapidly formed high density multilayers of compact cells that readily overgrew nontransformed cells. At the nonpermissive temperature (40 C) cell replication declined and division ceased after 4 days. Furthermore, at 40 C the cells grew as a monolayer and assumed a tetrahedral shape with a high cytoplasm-to-nucleus ratio, and displayed reduced ability to overgrow nontransformed cells. The transformed ovarian cells did not express detectable gonadotropin receptors and steroidogenic activity but retained their epithelial phenotype as demonstrated by cytokeratin staining of the cytoskeleton, the presence of microvilli, and the formation of tight junctions between cells. In support of the proposed autocrine-paracrine actions of IGF-I in the ovary, assay of conditioned serum-free culture medium revealed secretion of IGF-I-immunoreactive material by RGA-41S cells. HPLC-purified IGF-I immunoreactivity from these cells eluted with the same retention time as recombinant human IGF-I. When hybridized with a 32P-labeled rat IGF-I cDNA probe, poly(A)+ mRNA prepared from RGA-41S cells grown at both temperatures showed the typical three size classes of IGF-I mRNA on Northern blots (7.5, 1.7, and 0.8-1.2 kilobase kb), although the levels were somewhat higher at 33 C. The presence of IGF-I receptors in transformed cells was demonstrated by specific 125I-IGF-I binding to intact cells. Scatchard analysis indicated a single class of high affinity receptors at a density of 10(5) binding sites per cell and a dissociation constant (Kd) = 0.52 x 10(-9) M. Furthermore, hybridization of a 32P-labeled IGF-I receptor probe to Northern blots of poly(A+) RNA prepared from cells grown at 33 C and 40 C revealed an 11-kilobase rat IGF-I receptor mRNA. Physiological concentrations of IGF-I increased [3H]aminoisobutyric acid uptake by RGA-41S cells grown at either temperature, attesting to the retention of responsiveness to IGF-I in these transformed granulosa cells.(ABSTRACT TRUNCATED AT 400 WORDS)