Two proteins (ribophorins I and II), which are integral components of rough microsomal membranes and appear to be related to the bound ribosomes, were shown to be exposed on the surface of rat liver rough microsomes (RM) and to be in close proximity to the bound ribosomes. Both proteins were labeled when intact RM were incubated with a lactoperoxidase iodinating system, but only ribophorin I was digested during mild trypsinization of intact RM. Ribophorin II (63,000 daltons) was only proteolyzed when the luminal face of the microsomal vesicles was made accessible to trypsin by the addition of sublytical detergent concentrations. Only 30-40% of the bound ribosomes were released during trypsinization of intact RM, but ribosome release was almost complete in the presence of low detergent concentrations.Very low glutaraldehyde concentrations (0.005-0.02%) led to the preferential cross-linking of large ribosomal subunits of bound ribosomes to the microsomal membranes. This cross-linking prevented the release of subunits caused by puromycin in media of high ionic strength, but not the incorporation of [aH]puromycin into nascent polypeptide chains. SDS-acrylamide gel electrophoresis of cross-linked samples a preferential reduction in the intensity of the bands representing the ribophorins and the formation of aggregates which did not penetrate into the gels.At low methyl-4-mercaptobutyrimidate (MMB) concentrations (0.26 mg/ml) only 30% of the ribosomes were cross-linked to the microsomal membranes, as shown by the puromycin-KCl test, but membranes could still be solubilized with 1% DOC. This allowed the isolation of the ribophorins together with the sedimentable ribosomes, as was shown by electrophoresis of the sediments after disruption of the cross-links by reduction. Experiments with RM which contained only inactive ribosomes showed that the presence of nascent chains was not necessary for the reversible cross-linking of ribosomes to the membranes. These obser- 488J. CELL BIOLOGY 9 The Rockefeller University Press 9

We evaluated helminthic infection and anthropometric indicators of nutritional status in a group of school-age children from a slum area of Caracas, Venezuela. The proportions of children at or below the 10th percentiles for height/age and weight/age were significantly higher in those presenting helminthiasis than in those uninfected. Although this could partially reflect a codependence of both helminthic infection and undernutrition or poverty, when the children were administered regular anthelmintic treatment for a year their anthropometric values improved significantly. When they were re-evaluated 8 months after the end of anthelmintic administration, the degree of reinfection by the most common helminth, Ascaris lumbricoides, was significantly higher in the growth-retarded children. These results confirm the relationship between helminthic infection and decreased growth rates in underprivileged populations, and indicate that children at nutritional risk are more susceptible to such infections, even after a prolonged parasite-free period.

Rat liver microsomal glycoproteins were purified by affinity chromatography on concanavalin A Sepharose columns from membrane and content fractions, separated from rough microsomes (RM) treated with low concentrations of deoxycholate (DOC). All periodic acid-Schiff (PAS)-positive glycoproteins of RM showed affinity for concanavalin A Sepharose; even after sodium dodecyl sulfate (SDS) acrylamide gel electrophoresis, most of the microsomal glycoproteins bound [lzsI]concanavalin A added to the gels, as detected by autoradiography. Two distinct sets of glycoproteins are present in the membrane and content fractions derived from RM. SDS acrylamide gel electrophoresis showed that RM membranes contain 15-20 glycoproteins (15-22% of the total microsomal protein) which range in apparent mol wt from 23,000 to 240,000 daltons. A smaller set of glycoproteins (five to seven polypeptides), with apparent mol wt between 60,000 and 200,000 daltons, was present in the microsomal content fraction.The disposition of the membrane glycoproteins with respect to the membrane plane was determined by selective iodination with the lactoperoxidase (LPO) technique. Intact RM were labeled on their outer face with 1311 and, after opening of the vesicles with 0.05% DOC, on both faces with 125I. An analysis of iodination ratios for individual proteins separated electrophoretically showed that in most membrane glycoproteins, tyrosine residues are predominantly exposed on the luminal face of the vesicles, which is the same face on which the carbohydrate moieties are exposed. Several membrane glycoproteins are also exposed on the cytoplasmic surface and therefore have a transmembrane disposition. In this study, ribophorins I and II, two integral membrane proteins (mol wt 65,000 and 63,000) characteristic of RM, were found to be transmembrane glycoproteins. It is suggested that the transmembrane disposition of the ribophorins may be related to their possible role in ribosome binding and in the vectorial transfer of nascent polypeptides into the microsomal lumen. KEY WORDS rough microsomes 9The asymmetric distribution of molecular compotransmembrane glycoproteins concanavalin A nents within membranes enables these structures lactoperoxidase iodination 9 ribosome-binding to carry out their function as selective permeability sites barriers between the cell and its environment and 894 J. CELL BIOLOGY 9 The Rockefeller University Press 9 0021-9525/78/0901-089451.00 on