Effects of fat emulsions with different fatty acid composition on plasma and hepatic lipids in rats receiving total parenteral nutrition

Effects of different fatty acids on the development of hepatic steatosis were studied in rats receiving total parenteral nutrition (TPN). 65 rats, with internal jugular catheters, were divided into one control group (n = 8), and four experimental groups (n = 13-15 each). The control group was fed a chow diet and all experimental groups received TPN. TPN provided 300 kcal/kg/day with 40% of the non-protein energy provided as fat. All TPN solutions were isonitrogenous and identical in nutrient composition except for the fatty acid composition of the fat emulsion. Four kinds of fat emulsions rich in: 1) medium chain fatty acids (C8:0,C10:0), 2) oleic acid (C18:1 n-9), 3) linoleic acid (C18:2 n-6), 4) eicosapentaenoic acid (C20:5 n-3)/docosahexaenoic acid (C22:6 n-3), were used. These fat emulsions were prepared with: 1) a mixture of medium chain triglycerides (MCT) and soybean oil (9:1), 2) olive oil, 3) safflower oil, 4) fish oil, respectively. The results of the study demonstrated a higher hepatic lipid content in the olive oil and safflower oil groups than in the control group, whereas no significant difference was seen between the MCT and control groups. Also, no difference was observed between the fish oil and control groups. With regard to the plasma lipids, the MCT group and olive oil group produced hyperlipidaemia. The plasma of the safflower oil and fish oil groups, however, had a low lipid concentration comparable to the control group. These results suggest that TPN with a fat emulsion prepared with fish oil does not cause hyperlipidaemia nor induce hepatic steatosis in normal rats.

Lipoprotein responses to fish, coconut and soybean oil diets with and without cholesterol in the Syrian hamster

Thirty-six young male Syrian hamsters were fed with test diets containing coconut oil, soybean oil or fish oil with and without 0.5% cholesterol for 6 weeks. Without dietary cholesterol supplementation, animals on the fish oil diet had significantly lower plasma total triglyceride (TG) and total cholesterol than those on the coconut oil or soybean oil diet. The decrease of TG was seen mainly in the very low density lipoprotein (VLDL) fraction. The degree of decrease in cholesterol was similar in all of the lipoprotein fractions. With 0.5% dietary cholesterol supplementation, there was no significant difference in plasma TG level among the three dietary groups. However, the fish oil group had significantly higher plasma cholesterol than the coconut oil and soybean oil groups. The increase of cholesterol was mainly in the VLDL and low density lipoprotein (LDL) fractions. In contrast to the plasma cholesterol level, the hepatic cholesteryl ester content was significantly lower in the cholesterol-supplemented fish oil group than in the coconut oil and soybean oil counterparts. The cholesterol-supplemented fish oil group showed higher liver microsomal acyl-coenzyme A:cholesterol acyltransferase activity than the other two groups, while there was no significant difference in the excretion of fecal neutral and acidic sterols among the three dietary groups.

Effects of L-glutamine on induced hepatosteatosis in rats receiving total parenteral nutrition

Glutamine (Gln) supplementation in total parenteral nutrition (TPN) has been shown to have a preventive effect on high glucose induced hepatic steatosis. This animal study was undertaken to evaluate whether Gln could prevent hepatic steatosis induced by high fat or high glucose infusion. After placement of internal jugular catheters, rats were divided into three groups: control (n = 8), high fat (n = 13) and high glucose (n = 14) groups. The control group was fed with a chow diet and infused with saline alone. The experimental groups were infused with either a high fat (65% of nonprotein calories) or high glucose (83% of total kilocalories) solution. Energy intake was 35 kcal/100 g body weight per day. TPN solutions were isocaloric, isonitrogenous and isovolemic. Each experimental group was divided into two subgroups, with one receiving a Gln supplement to replace 40% of total amino acid nitrogen. The results demonstrated obvious fatty infiltration in the experimental groups, mainly from triglyceride (TG) accumulation. Plasma very low density lipoprotein-triglyceride (VLDL-TG) was significantly lower in the experimental groups than in the control group, suggesting that liver secretion of TG may have been inhibited in the experimental groups. Liver fatty acid synthetase (FAS) activity and plasma free fatty acid were lower in the high fat group than in the control and high glucose groups. There was no difference in hepatic lipids content, FAS activity, VLDL-TG, hepatic uptake of fatty acids and liver histologic change in the subgroups with and without Gln supplementation. Thus, Gln supplementation in a TPN solution has no effect in preventing hepatic steatosis induced by either high glucose or high fat infusion in rats under these experimental conditions.

Sources of triacylglycerol accumulation in livers of rats fed a cholesterol-supplemented diet

The source of free fatty acids (FFA) and the pathways contributing to the accumulation of neutral fats in livers of rats fed a cholesterol-enriched diet were investigated in this report. Supplementation with 1% cholesterol in the diet for four weeks resulted in hepatomegaly in the rats. The contents of cholesterol and triacylglycerols (TG) per gram liver measured in rats fasted overnight increased by 48 mg (approximately tenfold) and 66 mg (approximately fourfold), respectively. The activities of glycerophosphate acyltransferase and diacylglycerol acyltransferase, the two key enzymes for TG synthesis in liver microsomes, were found to increase by 23 and 19%, respectively, in the cholesterol-fed rats. The secretion of plasma TG present predominantly in very low density lipoprotein was found to decrease by approximately 30%. The incorporation of tritium from tritiated water in liver FFA increased by twofold in rats fed the cholesterol-supplemented diet, whereas the activity of CPT I in liver mitochondria decreased by 23%. The uptake of plasma FFA in vivo in livers of fasted rats maintained on the cholesterol-supplemented diet decreased by 60%. Our data thus indicate that the excess TG accumulated in livers of rats fed the cholesterol-enriched diet resulted from increased synthesis and decreased secretion of TG. To meet the demand of fatty acids for this purpose, de novo lipogenesis increased, whereas beta-oxidation decreased. Although difference in the uptake of extrahepatic FFA may be discounted, a difference in the uptake of chylomicron remnants between the control and cholesterol-fed rats may not be ruled out.

A novel stress-inducible metallothionein-like gene from rice

A novel rice genomic sequence encoding coding segments homologous to other metallothionein-like genes was isolated from Oryza sativa genomic library. This sequence, hereby designated as rgMT (rice genomic metallothionein-like gene), consists of two exons and one intron. From the coding sequence, it is predicted that rgMT encodes one protein of 74 amino acids. Differential expression of rgMT in rice plants was observed as mature transcripts were more abundant in roots than in leaves and sheaths. Under different stress conditions, such as excess heavy metals and heat shock, expression of rgMT was significantly elevated. This was especially noticeable with 250 microM CuCl2 for 16 h, 40 degrees C heat for 2 h and 0.06% DMSO for 1 h. Under sucrose starvation, rgMT transcripts also increased with time up to 72 h. During recovery from sucrose starvation, the transcripts declined slightly within 12 h of recovery. rgMT transcripts were also seen to have increased expression in senescent leaves. These results support the notion that rgMT is a stress-inducible gene in rice heretofore unreported.

The effects of apolipoprotein E polymorphism on the distribution of lipids and lipoproteins in the Chinese population

The effects of apolipoprotein E (apo E) polymorphism on the distribution of serum levels of total cholesterol (TC), triglyceride (TG), high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C) were studied in 546 unrelated Chinese in Taiwan. By isoelectric focusing and immunoblotting, three common alleles were demonstrated. The frequencies of the epsilon 2, epsilon 3 and epsilon 4 alleles were 0.076, 0.875 and 0.049, respectively. The relative frequency of the epsilon 3 allele was higher than that in Caucasians, whereas the frequency of epsilon 4 was lower in the Chinese population. Individuals with apo E4/4 phenotype had the highest serum TC and LDL-C concentrations, while the lowest levels were associated with apo E2/2 phenotype. There was a trend for individuals carrying the epsilon 2 allele to have a higher HDL-C level. No relationship between apo E phenotype and TG level was observed in this study. These data indicated that a given apo E allele acted in a relatively similar way in determining individual differences between Chinese and Caucasian populations in serum lipid and lipoprotein.

Transcripts of metallothionein genes in Arabidopsis thaliana

Using oligonucleotides with highly conserved cysteine-rich codons as probes, we isolated from a lambda YES Arabidopsis thaliana cDNA library two different sequences, each encodes an unique protein. These proteins, hereby designated as AtMT-q (AtMT-2) and AtMT-k (AtMT-1), are characteristic of metallothionein, carrying 13 and 14 cysteines in a total of 45 and 81 amino acids, respectively.

Replacement of all alpha-domain lysines with glutamates reduces metallothionein detoxification function

Mammalian metallothioneins (MTs) possess eight highly conserved lysine residues, including three in each of two metal binding domains. We used site-directed mutagenesis to replace these intradomain lysines in Chinese hamster ovary MT2 with glutamic acid and/or glutamine. These mutant MTs were expressed in a metal sensitive yeast host. One mutant which had all three lysines in the alpha-domain replaced by glutamates (K43,51,56E) exhibited a reduced ability, relative to native MT, to protect yeast transformants against otherwise toxic levels of cadmium. This triply substituted mutant also exhibited anomalous migration on a non-denaturing gel relative to wild type MT and other MT lysine mutants, suggesting that the intradomain lysines are important in maintaining the conformational integrity of MT.

Substitution of glutamic acids for the conserved lysines in the alpha domain affects metal binding in both the alpha and beta domains of mammalian metallothionein

Lysine residues are highly conserved in mammalian metallothioneins (MTs). Recombinant mutant Chinese hamster MT2 in which all of the lysines (K) in the alpha-domain were substituted by glutamic acids (E) was assayed with, expressed in and purified from a cadmium sensitive strain of yeast Saccharomyces cerevisiae. Circular dichroism analyses of the mutated protein, mutein K43,51,56E, revealed that the overall structure remained unchanged. However, a 1-D 113Cd NMR study detected significant differences in the chemical shifts of the corresponding resonances between wild type protein and the recombinant mutein. Reduction of integrated intensity in the NMR spectra was also observed for resonances from the four-metal cluster (I and V-VII) in the alpha-domain of the mutein. At various temperatures, facile intermolecular exchange of metals in the beta-domain of the mutein was also observed, which was unexpected and was different from wild type. Our results thus demonstrate that replacing all three lysines by glutamic acids in the alpha-domain changed metal-thiolate interactions in both domains of the recombinant mutein. This may explain the reduced ability of the mutein to convey cadmium resistance. We propose that while the lysine residues in the alpha-domain of wild type MT are not critical for maintaining protein structure, they play a role in regulating the microenvironment and stability of both metal-binding clusters, a feature critical to metal detoxification.

Effect of L-glutamine on hepatic lipids at different energy levels in rats receiving total parenteral nutrition

The effect of glutamine on hepatic steatosis and serum amino acid pattern was studied in rats receiving total parenteral nutrition (TPN) with different levels of caloric intake. Rats were divided into four groups; a control group (n = 10) was fed a chow diet and infused with saline only. Three experimental groups (n = 8 to 10) received TPN solutions at energy levels of 25 kcal, 30 kcal, and 35 kcal/100 g body weight, respectively. The experimental groups were maintained with TPN for a period of 6 days. Each experimental group was divided into two subgroups, one of which was supplemented with glutamine, replacing 40% of the total amino acid nitrogen. All of the basal TPN solutions were isonitrogenous and identical in nutrient composition, except for the difference in energy level, which was adjusted with glucose. The results demonstrated that liver fat increased in accordance with the increase of glucose supply, and this increase was mainly due to triglyceride accumulation. Very-low-density lipoprotein-triglyceride and serum free fatty acid were significantly higher in the 30-kcal groups. There were no differences in hepatic lipid content, very-low-density lipoprotein-triglyceride secretion, or hepatic uptake of fatty acids between subgroups with and without glutamine supplementation. It was concluded that glutamine enrichment of a TPN solution did not have any effect on hepatic steatosis in normal rats.

Cellular interactions implicated in the mechanism of photoreceptor degeneration in transgenic mice expressing a mutant rhodopsin gene

Photoreceptors of transgenic mice expressing a mutant rhodopsin gene (Pro347-->Ser) slowly degenerate. The mechanism of degeneration was studied by aggregation of embryos of normal and transgenic mice to form chimeras. In these chimeras, mosaicism was observed in the coat color, retinal pigment epithelium, and retina. In the retina, the genotype of adjacent patches of normal and transgenic photoreceptors was determined by in situ hybridization with a transgene-specific RNA probe. Photoreceptors in the chimeric retina degenerated uniformly, independent of the genotype and similar to the photoreceptors in transgenic mice. However, the chimeric retinas showed varying proportions of normal and transgenic cells. The chimeric retina with a nearly even proportion of normal and transgenic photoreceptors displayed uniform but slower degeneration than that observed in a transgenic mouse of the same age. Our results demonstrate non-autonomy of gene action for the mutated rhodopsin gene and imply that cellular interactions between photoreceptors in the retina probably play a role in degeneration.

Metallothionein detoxification function is impaired by replacement of both conserved lysines with glutamines in the hinge between the two domains

Mammalian metallothioneins (MTs) possess eight highly conserved lysine residues, two of which constitute the hinge between two metal binding domains. By site-directed mutagenesis and recombinant DNA techniques, we replaced the interdomain lysines in Chinese hamster ovary MT2 with all possible combinations of glutamic acid and/or glutamine. The resultant MTs were expressed and assayed for detoxification function in a transformed yeast system. Results showed that these mutant MTs, like the native protein, bound seven atoms of divalent metal per molecule and conferred cadmium resistance to a metal-sensitive yeast host. Replacement of one or both of the lysines in the interdomain region was inconsequential to the structure and function of MT, unless both substituted residues were uncharged. When both lysines were replaced by glutamine (K30,31Q), a reduction in the ability of MT to protect yeast transformants against otherwise toxic levels of cadmium was observed. This diminished metal detoxification capacity was due to a decrease in the steady-state level of MT. These results suggest that at least one charged amino acid must be present in the hinge for the proper expression of MT.

[Change and effect of Epstein Barr virus (EBV) antigen induced T8 cells in nasopharyngeal carcinoma patients and EBV seropositive individuals]

T8 cells from peripheral blood mononuclear cells (PBMC) of nasopharyngeal carcinoma (N PC) patients, IgA/VCA positive and negative normal individuals were induced by Epstein Barr virus (EBV) antigen, and their effects on the EBV infected auto-PBMC were observed. The data showed: after PBMC were induced by EBV antigen for 5 days, the T8 cells increased in the all three groups, but less remarkably in NPC group than in the other two groups. The T8 cells induced by EBV antigen could inhibit the activation, proliferation and differentiation of EBV infected auto-B cells in IgA/VCA positive and negative groups. But they had an enhancing effect in NPC group. The results suggest that the production of these cells was reduced and their function altered in NPC patients. Therefore it may be related to the enhancement of EBV activated B cells.

Foods predictive of nutrient intake in Chinese diet in Taiwan: I. Total calories, protein, fat and fatty acids

Dietary consumption data obtained by food weighing for 539 households in Taiwan in 1980-1981 were used to search for foods predictive of nutrient intake. The average per capita nutrient intake in each household was calculated for total calories, protein, fat and fatty acids (saturated fatty acids, oleic acid and unsaturated fatty acids). Stepwise multiple regression analysis was carried out to reveal the relative importance of each of 405 food items in the dietary survey data for predicting nutrient intake. We found that as few as seven to 20 food items could account for a large proportion of the variability of macronutrient intake in this population. These lists of foods were the minimum needed to categorize an individual's nutrient intake for epidemiological studies in Taiwan. The types and amounts of cooking oils (important predictors of fat and calories) added to the dishes were found to vary from family to family, and should be considered in designing dietary questionnaires for Chinese in other societies.

Foods predictive of nutrient intake in Chinese diet in Taiwan: II. Vitamin A, vitamin B1, vitamin B2, vitamin C and calcium

Dietary consumption data obtained by food weighing for 539 households in Taiwan in 1980-1981 were used to search for predictor foods of individual intake of several vitamins and calcium. Stepwise multiple regression analysis was carried out on food items that were univariately and significantly associated with nutrient intakes, to screen for the important predictors. Less than ten foods were enough to explain more than 90% of the interperson variation for vitamin A, vitamin B1, and vitamin B2. For vitamin C and calcium, 20 food items could explain only 87% of the variation. Salt, brown sugar, and soy bean sauce were selected among calcium predictors. The information on foods predictive of nutrient intake is useful in designing food frequency questionnaires and materials for nutrition education. Although this paper provides such information for Chinese living in Taiwan, some issues described (such as the need to assess spices) may have been overlooked and could be generalized to populations using stir-frying as a major cooking method.

The complete nucleotide sequence of the Crossostoma lacustre mitochondrial genome: conservation and variations among vertebrates

The complete mitochondrial (mt) genome of Crossostoma lacustre, a freshwater loach from mountain stream of Taiwan, has been cloned and sequenced. This fish mt genome, consisting of 16558 base-pairs, encodes genes for 13 proteins, two rRNAs, and 22 tRNAs, in addition to a regulatory sequence for replication and transcription (D-loop), is similar to those of the other vertebrates in both the order and orientation of these genes. The protein-coding and ribosomal RNA genes are highly homologous both in size and composition, to their counterparts in mammals, birds, amphibians, and invertebrates, and using essentially the same set of codons, including both the initiation and termination signals, and the tRNAs. Differences do exist, however, in the lengths and sequences of the D-loop regions, and in space between genes, which account for the variations in total lengths of the genomes. Our observations provide evidence for the first time for the conservation of genetic information in the fish mitochondrial genome, especially among the vertebrates.

Effects of dietary supplementation with fish oil on prostanoid metabolism during acute coronary occlusion with or without reperfusion in diet-induced hypercholesterolemic rabbits

We studied the changes in myocardial and aortic concentrations of prostacyclin and thromboxane A2 during acute coronary occlusion with or without reperfusion in rabbits fed with a cholesterol-enriched diet with or without fish oil supplementation for a short (5 days) or long period (6 weeks). New Zealand white male rabbits were divided into 5 groups: Group I, 15 control rabbits fed with a laboratory standard rabbit chow. In addition to the standard chow, the 4 study groups were treated with cholesterol or fish oil. Group II, 17 rabbits fed with a 1% high cholesterol diet for 5 days. Group III, 16 rabbits fed with a diet containing 1% cholesterol and 10% fish oil for 5 days. Group IV, 17 rabbits fed with the same diet as group II for 6 weeks. Group V, 18 rabbits fed with the same diet as group III for 6 weeks. Each group of rabbits was randomly divided into the coronary occlusion or occlusion-reperfusion mode of experiment. Acute coronary occlusion was induced by ligating the marginal branch of the left circumflex coronary artery for 1 h. Subsequent reperfusion for 4 h was performed in the occlusion-reperfusion rabbits. The aortic tissue above the aortic valve and the ischemic and normal (nonischemic) areas of the left ventricle were excised for the measurement of 6-keto-PGF1 alpha and thromboxane B2 levels by radioimmunoassay. Both during coronary occlusion and occlusion-reperfusion, rabbits showed higher myocardial concentrations of 6-keto-PGF1 alpha and thromboxane B2 in the ischemic area than in the normal myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy requirements in response to high protein feeding in young male adults

Two experiments were conducted to investigate the effects of moderate (MPI) and high (HPI) levels of protein intake on energy utilization in 12 healthy young male adults who were confined to a metabolic unit for 56 days. The amount of energy supplied was adjusted so that the subjects could maintain a relatively constant body weight, which was used as the criterion to see whether the body was under an energy balance. All foods were supplied in conventional style. In the first experiment, six young men were given a diet of 1.18 g (MPI) and 1.74 g (HPI) protein/kg of body weight/day in consecutive periods. In the second experiment, another six young men were studied at a protein intake of 1.08 g (MPI) and 2.00 g (HPI)/kg/day. The results indicate that both energy intake and energy expenditure are independent of protein intake. The average gross energy intake of the subjects was between 2,300 to 3,240 kcal/day, corresponding to a light-to-moderate grade of energy expenditure. The efficiency of energy utilization did not differ significantly between the moderate and high levels of protein intake in adults.

Effects of excess protein intake on nitrogen utilization in young men

The efficiency of nitrogen (N) utilization was studied in 12 young male subjects. Protein intake levels were adjusted from moderate (1.08 and 1.18 g protein/kg/day) to high (1.74 and 2.00 g protein/kg/day). All of the food was supplied in the form of a normal mixed Chinese diet. Six subjects were admitted to a metabolic unit at a time for 56 days, in two consecutive periods. The results indicate that a higher protein intake causes more N excretion in urine and feces. Biologic value (BV) and net protein utilization (NPU) were markedly decreased during the high protein intake (HPI) period. However, a significant increase in the N balance was found in the presence of excessive protein intake. Digestibility of protein seemed to increase during the HPI period, with the apparent digestibility of the dietary protein being about 83% to 90%. We conclude from this study that excessive N intake reduces the efficiency of N utilization, but still results in a positive N balance in adult human subjects.

Effects of dietary supplementation with fish oil on atherosclerosis and myocardial injury during acute coronary occlusion-reperfusion in diet-induced hypercholesterolemic rabbits

We studied myocardial injury during acute coronary occlusion-reperfusion and atherosclerosis in rabbits fed a high cholesterol diet with or without fish oil supplementation. New Zealand white male rabbits were divided into 3 groups. Eight control rabbits fed with laboratory standard rabbit chow were group I. In addition to the standard chow, 15 rabbits fed with a 1% cholesterol-enriched diet for 6 weeks were group II, and 10 rabbits fed with a 1% cholesterol-enriched and 10% fish oil supplemented diet for 6 weeks were group III. Acute coronary occlusion was induced by ligating the marginal branch of the left circumflex coronary artery for 1 h, followed by reperfusion for 4 h. Myocardial injury was assessed by tissue creatine kinase activities and amino-nitrogen concentrations from the ischemic (infarct) and nonischemic (normal) myocardium, and the infarct area/risk area ratios of the left ventricle. The surface area of the atherosclerotic lesions of the aorta and pulmonary artery was measured by planimeter. There was significantly more myocardial loss of creatine kinase and amino-nitrogen in the cholesterol-fed rabbits than the controls (p less than 0.01 and 0.02, respectively). The cholesterol and fish oil-treated rabbits had a nonsignificant reduction in myocardial loss of both agents as compared to their corresponding cholesterol-fed ones. The same trend was also found in the infarct area/risk area ratio. Fish oil treated rabbits had a good effect on the reduction of atherosclerotic lesions and tissue cholesterol levels in the aorta and pulmonary artery, but not in the left ventricle.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effect of adrenalectomy on rat liver metallothionein mRNA levels in basal and stress conditions

Liver metallothionein (MT) mRNA and serum MT levels of adrenalectomized (ADX) and sham-ADX rats in basal and stress (1, 3 or 6 h of restraint) conditions have been measured. Serum MT levels were overall lower in ADX than in sham-ADX rats. Basal liver MT mRNA levels were increased in ADX rats, suggesting that glucocorticoids have an inhibitory role on the regulation of liver MT synthesis. In contrast, liver MT mRNA levels were increased by stress in sham-ADX but not in ADX rats, suggesting a stimulatory role for glucocorticoids. These results suggest that glucocorticoids have a different role in liver MT regulation depending on the physiological situation.

Mutation of invariant cysteines of mammalian metallothionein alters metal binding capacity, cadmium resistance, and 113Cd NMR spectrum

Using a yeast expression vector system, we have expressed both wild type and six mutated Chinese hamster metallothionein coding sequences in a metal-sensitive yeast strain in which the endogenous metallothionein gene has been deleted. The mutant proteins have single or double cysteine to tyrosine replacements (C13Y, C50Y, and C13,50Y), single cysteine to serine replacements (C13S and C50S), or a single cysteine to alanine replacement (C50A). These proteins function in their yeast host in cadmium detoxification to differing extents. Metallothioneins which contain a cysteine mutation at position 50 (C50Y, C50S, C50A, and C13,50Y) conferred markedly less cadmium resistance than wild type metallothionein, or metallothionein with a single cysteine mutation at position 13 (C13Y and C13S). Wild type and three of the mutant Chinese hamster metallothioneins (C13Y, C50Y, and C13,50Y) were purified from yeast grown in subtoxic levels of either CdCl2 or 113CdCl2. All three of the mutant proteins bound less cadmium than the wild type protein when metal-binding stoichiometries were determined. The one-dimensional 113Cd NMR spectrum of the recombinant wild type Chinese hamster metallothionein was compared to the spectra of native rat and rabbit liver metallothioneins. The close correspondence between the 113Cd chemical shifts in these metallothioneins is consistent with the presence of two separate metal clusters, A and B, corresponding, respectively, to the alpha- and beta-domains, in the recombinant metallothionein. The one-dimensional 113Cd NMR spectra recorded on each of the three mutant metallothioneins, on the other hand, provide some indication as to the structural basis for the reduced, by one, metal stoichiometry of each of the mutant metallothioneins. For the C13Y mutant, it appears that the beta-domain now binds a total of two metal ions whereas with the C50Y mutant, the alpha-domain appears metal-deficient. For the double mutant, C13,50Y, the 113Cd resonances are indicative of major structural reorganizations in both domains.

Molecular cloning of Chinese hamster metallothionein II gene and its 5' flanking region

A genomic DNA clone containing Chinese hamster metallothionein II (MTII) gene and its 5' flanking region was isolated from Cd resistant Chinese hamster ovary (CHO) cells. DNA sequence analysis showed that there are three exons and two introns in the structure of the MTII gene. Further characterization of the 5' flanking region reveals the possible transcription initiation site, metal responsive element and basal-level enhancer sequence. Putatively, this is the promoter region of CHO MTII gene.

Effect of cysteine replacements at positions 13 and 50 on metallothionein structure

Recombinant wild-type and mutant Chinese hamster metallothioneins, purified from the yeast Saccharomyces cerevisiae, were analyzed for their chemical and spectroscopic properties. The mutant proteins contain cysteine to tyrosine replacements at positions 13 and 50. Wild-type and mutant metallothioneins, in their cadmium-bound forms, all showed characteristic ultraviolet absorption spectra with shoulders at 245-250 nm due to cadmium-thiolate charge transfer. Upon acidification, these absorption shoulders were abolished. In all cases, two distinct titrations were seen, presumably corresponding to two independent cadmium binding domains in each of the proteins. Analysis of domain structures was performed both with the sulfhydryl reagent 5,5'-dithiobis(2-nitrobenzoic acid) and with the protease subtilisin. These studies indicated that both mutations affected domain structure by disrupting the normally tight protein clusters. Circular dichroism spectra obtained for wild-type and mutant metallothioneins showed unique structural rearrangements in mutants containing a cysteine-50 to tyrosine alteration. These data, along with previously obtained 113Cd NMR data, were incorporated into a model which can account for the in vivo and in vitro properties of these mutant proteins.