The effect of down-regulation on the intracellular pool of insulin receptors and the role of glycosylation in recovery from down-regulation have been studied in fibroblastic cultures from the skin of non-diabetic mice. In control cultures, 55% of the total specific [125I]insulin-binding activity was in the intracellular compartment. Insulin caused a time- and concentration-dependent decrease in the number of cell surface insulin receptors, with no significant change in total insulin receptors. This decrease in surface receptors was accompanied by an increase in the specific binding of [125I]insulin in the intracellular compartment. Removal of insulin from down-regulated cells resulted in a time-dependent increase in the binding of [125I]insulin to surface receptors, reaching 90% of that in controls by 12 h. The recovery of surface insulin receptors after removal of insulin was blocked by incubation of cultures with tunicamycin, but not by cycloheximide. These results indicate that down-regulation of surface insulin receptors by insulin is associated with translocation of receptors into the intracellular pool and suggest that protein glycosylation is important in insulin receptor recycling and externalization.

Arginine has been demonstrated to be a potent stimulus to GH and PRL secretion. To determine the effect of arginine on plasma ovine placental lactogen (oPL) concentrations, arginine (50 g in 350 ml distilled water, pH 7.4) or hypertonic saline of identical volume, osmolality, and pH was infused iv over a 30-min period into nine pregnant ewes, and blood samples from chronic indwelling venous catheters were obtained at frequent intervals before and for 8 h after the infusions. After the infusion of hypertonic saline, plasma oPL concentrations (measured by homologous RIA) decreased 20--50% over 1--2 h and then returned to baseline concentrations. After the infusion of arginine, plasma oPL concentrations also decreased by 20--50% for 1--2 h. However, 2--3 h after the infusion, plasma oPL concentrations in creased 79--115% (delta = 204--700 ng/ml) over preinfusion concentrations in seven ewes and 454% (2930 ng/ml) and 1142% (2042 ng/ml) in two ewes and remained elevated for the remainder of the 8-h interval. When the amount of arginine infused was reduced from 50 to 25 g, an increase in plasma oPL concentrations occurred in only one of five ewes. Plasma oPL concentrations increased by 8--58% after infusions of 50 g alanine or glycine but did not increase after 50 g glutamic acid. The delayed oPL response to arginine suggests that the increase in plasma oPL concentrations is not caused directly by arginine but rather by changes in the synthesis, secretion, and/or degradation of oPL induced indirectly by arginine.

Ovine placental lactogen (oPL) and bovine growth hormone (bGH) increase the circulating concentration of somatomedin in hypophysectomized rats. This finding indicates that some of the somatotropic properties of oPL may be due to the induction of somatomedin and raises the possibility that oPL has a role in the control of fetal growth.

The covalent structure of apolipoprotein A-II, isolated from the serum high-density lipoprotein of a single male Rhesus monkey (Macaca mulatta), was determined. The amino acid sequence of this 77-residue polypeptide is: less than Glu-Ala-Glu-Glu-Pro5-Ser-Val-Glu-Ser-Leu10-Val-Ser-Gln-Tyr-Phe15-Gln-Thr-Val-Thr-Asp20-Tyr-Gly-Lys-Asp-Leu25-Met-Glu-Lys-Val-Lys30-Ser-Pro-Glu-Leu-Gln35-Ala-Gln-Ala-Lys-Ala40-Tyr-Phe-Glu-Lys-Ser45-Lys-Glu-Gln-Leu-Thr50-Pro-Leu-Val-Lys-Lys55-Ala-Gly-Thr-Asp-Leu60-Val-Asn-Phe-Leu-Ser65-Tyr-Phe-Val-Glu-Leu70-Arg-Thr-Gln-Pro-Ala75-Thr-Gln-COOH. A comparison of this structure to that of the monomeric form of human apolipoprotein A-II reveals a high degree of homology except for six conservative amino acid replacements (positions 3, 6, 40, 53, 59, and 71). Of particular structural significance is the replacement of cysteine by serine in position 6. This explaines why Rhesus A-II exists in monomeric form, contrary to the established dimeric nature of the human protein.

An enzyme has been obtained from bovine pituitary tissue which hydrolyzes L-pyrrolidonecarboxylyl- L-alanine, but not L-glutamyl-Lalanine. The enzyme was identified in whole pituitary homogenates, in 100,000 × g supernatant fraction of whole pituitaries and in anterior pituitary homogenates. After partial purification by ammonium sulfate precipitation and gel filtration, the enzyme was found to have a Km of 2.3 × 10–4M and to have maximal activity at pH 7.3. Like the Pseudomonas fluorescens pyrrolidonecarboxylyl peptidase prepared by Doolittle and coworkers, this enzyme is sulfhydryl-dependent and unstable in solution, but may be stabilized ∧ with the inhibitor 2-pyrrolidinone. The pituitary enzyme has been shown to cleave L-2-pyrrolidone- 5-carboxylic acid from the NH2-terminal position of synthetic thyrotropin-releasing factor and thus may have a degradative function related to the regulatory system controlling release of thyroid-stimulating hormone from the anterior pituitary. Evidence has been obtained for a similar peptidase in human pituitary homogenates. (Endocrinology93: 1428,1973

Purified bovine growth hormone (bGH) and human growth hormone (hGH) have been covalently bound to Sepharose 4B gel utilizing cyanogen bromide as the activating agent. Under the conditions employed, up to 1.44 mg of bGH and 1.20 mg of hGH were covalently bound per ml of settled Sepharose. Although growth hormone linked to Sepharose retained immunological activity in the complement fixation assay, the curve was significantly shifted in the direction of higher antigen concentrations and a zone of antigen excess was not attained with bGH—Sepharose. The observation that mixtures of unconjugated bGH or hGH and Sepharose gave complement fixation curves similar to that for bGH or hGH alone confirms that the covalent binding of growth hormone directly to Sepharose is accompanied by structural changes in the hormone or steric effects which alter the reactivity of the antigenic sites. This, however, did not interfer with the use of the bGHand hGH—Sepharose conjugates for purification of specific antibody from antisera. Purified antibody, eluted from appropriate columns of immobilized hormone with guanidine hydrochloride, reacted normally with unconjugated growth hormone by immunodiffusion and in the complement fixation assay. (Endocrinology92: 431, 1973)

B oth β‐thalassaemia and α‐thalassaemia have been described in Oriental Jews (Matoth, Shamir and Freundlich, 1955; Ramot, Sheba, Fisher, Ager and Lehmann, 1959) and an abnormal methaemoglobin has been found by Mani, Kende and Ramot (1962) in a Polish Jewish family. No other abnormal adult haemoglobin has, however, yet been found in either Oriental or Western Jews. We should like to report a haemoglobin variant in an Ashkenazi (Western‐Jewish) family that came to Israel from Poland. In addition to its being an unusual observation in Jews, the variant itself has not been observed before. It resembles in its electrophoretic behaviour the haemoglobin L described in Indians by Ager and Lehmann (1957), but differs from L in its chromatographic properties and in the location of the mutational change within the globin moiety.