Cholesterol metabolism and sterol carrier protein-2 (non-specific lipid transfer protein)

Hepatic sterol carrier protein-2 significantly enhances the microsomal conversion of cholesterol to 7 alpha-hydroxy-cholesterol. In the present work we have attempted to correlate the hepatic content of sterol carrier protein-2 with bile acid formation. We have determined the amount of this protein in a variety of physiological and experimental conditions, in which the rate of bile acid synthesis varies over a wide range, viz. during fetal development, in inbred strains of rats with different rates of bile acid synthesis, and in rats fed diets containing drugs which modify the rate of bile acid synthesis. The outcome of these experiments does not support the idea that sterol carrier protein-2 has any association with bile acid synthesis. From our data we further conclude that hepatic sterol carrier protein-2 is an adaptable protein because its level increases during development from the fetal to the post-weaning stage of the rat and since it can be modulated by oral administration of certain drugs. Furthermore, it is demonstrated that the level of sterol carrier protein-2 varies between six inbred strains of rats.     

Properties and possible function of phosphatidylinositol-transfer proteins

It is proposed that the phosphatidylinositol-transfer protein (PI-TP) may function as a carrier of phosphatidylinositol (PI) in the cell. PI-TP occurs in all mammalian tissues examined and appears to be strongly conserved. Its intracellular distribution was studied by immunoblotting and immunofluorescence techniques. PI-TP displays a dual specificity in that it preferentially transfers PI over phosphatidylcholine (PC) between membranes. Its lipid binding site and transfer characteristics were investigated with fluorescent PI and PC analogues containing parinaroyl- and pyrenylacyl-labeled chains. PI-TP is ideally suited for maintaining PI levels in intracellular membranes, possibly the plasma membrane.     

The structure and evolution of the spider monkey delta-globin gene

We have isolated the delta-globin gene of the New-World spider monkey, Ateles geoffroyi, and compared its nucleotide sequence with those of other primate delta- and beta-globin genes. Among primate delta-globin genes, the rate of nonsynonymous substitutions is much less than the rate of synonymous substitutions. This suggests that primate delta- globin genes may remain under evolutionary conservation, perhaps because hemoglobin A2 has an as yet unknown physiological importance.      

Intracellular redistribution of SCP2 in Leydig cells after hormonal stimulation may contribute to increased pregnenolone production

Sterol carrier protein2 (SCP2) also designated non specific lipid transfer protein (nsL-TP), added to tumour Leydig cell mitochondria as a pure compound or in cytosolic preparations, stimulates pregnenolone production two- to three-fold. This stimulation can be abolished by addition of anti rat SCP2 but not by preimmune IgG-antibodies. SCP2- levels in the cytosol are increased in less than two minutes after addition of lutropin (LH). This increased SCP2 level may contribute to stimulation of steroid production in intact cells. After hormonal stimulation the subcellular distribution of SCP2 changes. A two-fold increase of SCP2- levels in the supernatant fraction and four-fold decrease in extracts of the particulate fraction was observed 30 min after stimulation of tumour Leydig cells with LH and subsequent fractionation. This apparent shift of SCP2 can be explained by an altered association with membranes or a true relocation of the protein from the particulate to the supernatant fractions under the influence of the hormone.     

Differentiation of keratinocytesin vitro: a new culture vessel mimicking thein vivo situation

A culture vessel consisting of two independent chambers separated only by the growth substrate is described. Cells may be cultured on both sides of the growth substrate. Culture medium and gas exposure can independently be controlled in both compartments. Human hair follicles have been used as source of keratinocytes and the bovine eye lens capsule has been explored as growth substrate. The presence of 5% CO₂ in air in the lower compartment appears to have a significant effect on the morphology of the cultures. When the cultures are being exposed to air with 5% CO₂, the culture medium being applied in the lower compartment, formation of corneocytes characteristic for adult stratum corneum is induced, as evidenced by light and electron microscopy. To the knowledge of the authors, this stage of differentiationin vitro has not been obtained with previously described systems. Differentiation of the lower cell layers has been characterised with specific antibodies. The possible use of the system for applied and pure scientific research is discussed.     

Biochemical pathways in prokaryotes can be traced backward through evolutionary time

For the first time, a credible prokaryotic phylogenetic tree is being assembled by Woese and others using quantitative sequence analysis of oligonucleotides in the highly conservative rRNA. This provides an evolutionary scale against which the evolutionary steps that led to the arrangement and regulation of contemporary biochemical pathways can be measured. This paper presents an emerging evolutionary picture of aromatic amino acid biosynthesis within a large superfamily assemblage of prokaryotes that is sufficiently developed to illustrate a new perspective that will be applicable to many other biochemical pathways.      

An improved technique for the demonstration of glycogen depleted skeletal muscle fibres

Several technical difficulties have been overcome in the use of Lowicryl 4KM resin. In order to embed and section tissue satisfactorily in the resin, it has been found necessary to thoroughly degass the resin before infiltration and polymerisation. After irradiation with UV light, the blocks are further polymerised by exposure to daylight for 2-3 weeks and then stored under partial vacuum over dessicant.     

Sterol carrier protein 2 (non-specific lipid transfer protein) is localized in membranous fractions of Leydig cells and Sertoli cells but not in germ cells.

The cellular and subcellular distribution of sterol carrier protein 2 (SCP2; nsL-TP) was reinvestigated in rat testicular cells by Western blotting and immunocytochemistry, using the affinity purified antibody against rat liver SCP2. Western blot analysis revealed high levels of the protein in the somatic cells of the testis, e.g., Leydig and Sertoli cells whereas it could not be detected in germ cells. This cellular localization of SCP2 was confirmed by Northern blotting. Immunocytochemical techniques revealed that in Leydig cells, immunoreactive proteins were concentrated in peroxisomes. Although SCP2 was also detected in Sertoli cells, a specific subcellular localization could not be shown. SCP2 was absent from germ cells. Analysis of subcellular fractions of Leydig cells showed that SCP2 is membrane bound without detectable amounts in the cytosolic fraction. These results are at variance with data published previously which suggested that in Leydig cells a substantial amount of SCP2 was present in the cytosol and that the distribution between membranes and cytosol was regulated by luteinizing hormone. The present data raise the question in what way SCP2 is involved in cholesterol transport between membranes in steroidogenic cells but also in non-steroidogenic cells.