Potassium-mediated stimulation of hepatic glycogenolysis

Increased extracellular potassium concentrations ([K+]o) stimulated transient increases in glucose release and 45Ca2+ washout in the perfused rat liver. Stimulated glucose release had a K0.5 of about 26 mM for [K+]o, was not desensitized by successive infusion intervals of increased [K+]o, was not affected by altering the direction of perfusion, was absolutely dependent on the presence of [Ca2+]o, and was blocked by 2 mM cobalt or 10 microM verapamil. The increase in 45Ca2+ washout resulting from increased [K+]o also was blocked by 2 mM cobalt or 10 microM verapamil. Inhibitors of vascular tone (nitroprusside, atriopeptin II), arachidonic acid metabolism (indomethacin, nordihydroguaiaretic acid), and alpha- or beta-adrenergic or muscarinic nerve stimulation/secretion (phentolamine, propranolol, atropine) were unable to inhibit the [K+]o-stimulated glucose release. ATP, ADP, and AMP concentrations in tissue freeze-clamped 2 min after the onset of infusion of 50 mM K+ were not significantly different from control tissue. Glucose release from freshly isolated suspensions or primary cultured monolayers of hepatocytes or from liver slices, all of which responded to glucagon or phenylephrine, did not respond to increased [K+]o. The results indicate that glycogenolysis stimulated by depolarizing gradients of K+ is dependent on an intact perfused vasculature and may be mediated by potential-sensitive Ca2+ channels present in the vascular endothelium of the liver.     

The enzyme defect in bovine protoporphyria. Studies with purified ferrochelatase

Ferrochelatase was purified from the livers of normal and protoporphyria cattle by chromatography on Blue Sepharose CL-6B in order to investigate the enzyme defect in this disorder. The increase in specific activity (up to 2900-fold) indicated that the normal and protoporphyria enzymes were purified to a similar degree. The mutant enzyme had catalytic activity which was 10 to 15% of normal ferrochelatase, although the Michaelis constants for protoporphyrin and iron were similar. The molecular mass of the normal and protoporphyria enzyme protein was 40 kDa as evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In the presence of 15 mM sodium cholate, gel filtration demonstrated a similar size. However, at a lower concentration of sodium cholate (4 mM) the molecular mass was about 240 kDa, suggesting that the purified enzymes aggregate under this condition. Polyvalent antibodies were raised in rabbits using as antigens purified normal native enzyme and normal 40-kDa protein which had been further purified by preparative SDS-PAGE. In Western blots these antibodies complexed with both the normal and mutant 40-kDa proteins. The amount of 40-kDa protein in normal and protoporphyria mitochondrial fractions was also similar as evaluated by Western blots. These studies indicate that the ferrochelatase defect in bovine protoporphyria probably results from a point gene mutation that causes a minor change in enzyme structure.     

Regulation of DNA synthesis in human fetal hepatocytes by placental lactogen, growth hormone, and insulin-like growth factor I/somatomedin-C

Hepatocytes were isolated by gentle collagenase digestion of liver fragments from human fetuses of 8-16 weeks gestation obtained following prostaglandin-induced pregnancy terminations. They were maintained on collagen-coated tissue culture dishes in selective arginine-free medium for up to 72 hr, and the action of hormones and growth factors on DNA synthesis was studied by autoradiography following incubation with 3H-thymidine. The labeling index of hepatocytes was consistently enhanced by 25-250 ng/ml human placental lactogen (HPL), 25-250 ng/ml human growth hormone (HGH), 10-50 ng/ml insulin-like growth factor I/somatomedin-C (IGF I/Sm-C), and 10% dialyzed fetal calf serum, reaching a maximum of three- to four-fold greater than in basal medium alone. Under basal conditions, 30% of hepatocytes stained positively for the presence of IGF peptides using a monoclonal antibody raised against purified human IGF I/Sm-C. Although this proportion did not change following treatment with HGH and HPL, IGF I/Sm-C released by cells into culture medium was considerably increased in the presence of both hormones. Incubation with the SmC 1.2 monoclonal antibody abolished the increase in labeling index in response to IGF I/Sm-C and partially blocked the response to both HPL and HGH. These results indicate that both HPL and HGH stimulate DNA synthesis in human fetal hepatocytes and suggest that this effect is at least partly indirect through the release and paracrine action of IGF I/Sm-C.     

Pliocene hominid partial mandible from Tabarin, Baringo, Kenya

Sediments in the Tugen Hills, west of Lake Baringo, Kenya, form one of the best fossiliferous successions known in Africa spanning the period from 14 my to less than 4 my. Hominoid fossils have previously been recovered from a number of localities in the region. We describe here a new hominid mandible (KNM-TH 13150) from the site of Tabarin, in the Chemeron Formation. Isotopic determinations on a tuff below the fossiliferous horizon gives dates of 4.96 my and 5.25 my. The associated fauna is consistent with these results and independently suggests a minimum age for the specimen of 4.15 my. Although fragmentary, the preserved morphology of the Tabarin mandible is consistent with the diagnosis of the Pliocene hominid Australopithecus afarensis. It can be distinguished from all other currently recognized hominoid taxa.     

Development of High-Frequency Delivery System for Transposon Tn919 in Lactic Streptococci: Random Insertion in Streptococcus lactis subsp. diacetylactis 18-16

The conjugative transposon Tn919, originally isolated in Streptococcus sanguis FC1, is capable of low-frequency transfer (10⁻⁷ and 10⁻⁸ per recipient) on membrane filters to a wide number of streptococcal recipients including the industrially important lactic streptococci. The introduction of pMG600 (Lac⁺ Lax⁻; a lactose plasmid capable of conjugative transfer at high frequencies and which, in certain hosts, confers an unusual clumping phenotype) into a Streptococcus lactis CH919 donor, generating S. lactis CH001, resulted in a significant improvement in the transfer frequency of Tn919 to S. lactis CK50 (1.25 × 10⁻⁴ per recipient). In addition, these matings could be performed on agar surfaces, allowing the recovery of a greater number of recipients than with filter matings. Tn919 also transferred at high frequency to S. lactis subsp. diacetylactis 18-16S but not to Streptococcus cremoris strains. Insertion in 18-16S transconjugants generated from filter matings with an S. lactis CH919 donor was random, occurring at different sites on the chromosome and also in plasmid DNA. Thus, the conditions necessary for the practical exploitation of Tn919 in the targeting and cloning of genes from a member of the lactic streptococci, namely, high-frequency delivery and random insertion in host DNA, were achieved.     

The kinetics of milk coagulation: IV. The kinetics of the gel-firming process

A mechanistic kinetic model of gel firmness development during milk gel formation is presented. The model correctly accounts for the influence of enzymatic kappa-casein hydrolysis on the rate of firmness development in renneted milk gels. The model used is based on two first-order reactions occurring in series. The first reaction is enzymatically controlled and corresponds to the formation of gel crosslink sites by kappa-casein hydrolysis. The second reaction is nonenzymatic and corresponds to the process of crosslink formation and depletion of active sites. The model successfully predicts gel firmness development in the temperature range 31-45 degrees C for a variety of initial enzyme concentrations.     

Seasonal variation in diagnostic enzymes and biochemical constituents of captive northern bobwhites and passerines

1. A variety of biochemical measurements were taken periodically in captive northern bobwhite (Colinus virginianus L.), European starlings (Sturnus vulgaris L.), red-winged blackbirds (Agelaius phoeniceus L.) and common grackles (Quiscalus quiscula L.) to determine whether baseline values remain sufficiently stable throughout the year for general clinical use in the absence of concurrent control specimens. 2. Variables included whole blood hematocrit and hemoglobin, plasma lactate dehydrogenase, alpha-hydroxybutyrate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, creatine kinase, butyrylcholinesterase, alkaline phosphatase, glucose, albumin, total protein, creatinine, urea nitrogen, uric acid, cholesterol, and triglycerides, and brain acetylcholinesterase. Butyryl- and acetylcholinesterase were included because of their specific uses in toxicology. 3. Significant seasonal differences were detected for each of the variables except brain acetylcholinesterase in at least one of the species. Significant species differences were detected during at least one season for all of the variables measured. 4. All species were maintained outdoors, but only northern bobwhites came into reproductive condition and showed sex-differences in the clinical variables during their normal breeding season. 5. It was concluded that reference values for the 18 clinical variables measured could be calculated from our data for adult specimens of the species studied, and that results for one species cannot be extrapolated with certainty to any other species. 6. Estimated normal bounds for each of the 18 variables measured by commonly used clinical procedures are presented for reproductively quiescent northern bobwhites, European starlings, red-winged blackbirds, and common grackles.     

KIN, a mammalian nuclear protein immunologically related to E. coli RecA protein

A polypeptide of about 120 kDa, called KIN, has been identified in rat FR 3T3 cells by immunoblotting using affinity-purified antibodies against the RecA protein of Escherichia coli (38 kDa). The KIN protein as shown by fluorescent light microscopy and electron microscopy is essentially concentrated in the nucleus. Its level is higher in proliferating than in quiescent cells. Cell treatment with mitomycin C increases the level of the KIN protein. We sought similar proteins in other mammalian cells. Proteins with the same electrophoretic mobility were detected in mouse, monkey and human cell lines as well as in rat and mouse embryos.