Zinc deficiency and lung converting enzyme activity in rats

Summary Angiotensin converting enzyme activity was found to be significantly decreased in the isolated perfused lung from zinc-deficient rats when compared with that of controls. Addition of zinc ion to the superfusion medium did not cause a recovery in this decreased activity of the enzyme. It is postulated that zinc deficiency probably produces a structural change in the lung angiotensin converting enzyme.This work is supported by a grant from Turkish Scientific and Technical Research Council (TAG-350).     

Angiotensin I converting enzyme activity in pulmonary tissue of fetal and newborn rabbits

Summary Angiotensin I converting enzyme in pulmonary tissue of fetal and newborn rabbits was measured using Hip-His-Leu as substrate. Enzyme activity was detected in the late fetal period, increased gradually until birth and increased markedly after birth. Enzyme activity reached adult levels on the 2nd and 3rd day after birth. This observations suggests that the metabolic activity of the lung for angiotensin develops suddenly at the time of derivery.This work was supported in part by grant No. 187032 from Ministry of Education.     

Active-site mutants of class B beta-lactamases: substrate binding and mechanistic study

Increased resistance to β-lactam antibiotics is mainly due to β-lactamases. X-ray structures of zinc β-lactamases unraveled the coordination of the metal ions, but their mode of action remains unclear. Recently, enzymes in which one of the zinc ligands was mutated have been characterized and their catalytic activity against several β-lactam antibiotics measured. A molecular modeling study of these enzymes was performed here to explain the catalytic activity of the mutants. Coordination around the zinc ions influences the way the tetrahedral intermediate is bound; any modification influences the first recognition of the substrate by the enzyme. For all the studied mutants, at least one of the interactions fails, inducing a loss of catalytic efficiency compared to the wild type. The present studies show that the enzyme cavity is a structure of high plasticity both structurally and mechanistically and that local modifications may propagate its effects far from the mutated amino acid. Received 28 August 2002; received after revision 22 October 2002; accepted 24 October 2002 RID="*" ID="*"Corresponding author.     

Testosterone derivatives are neuroprotective agents in experimental diabetic neuropathy

In this study we have assessed the effect of testosterone (T), dihydrotestosterone (DHT) and 5αandrostan-3α, 17β-diol (3α-diol) therapies on diabetic neuropathy. Diabetes was induced in adult male rats by the injection of streptozotocin and resulted in decreased T and increased 3α-diol levels in plasma and in decreased levels of pregnenolone and DHT in the sciatic nerve. Moreover, a reduced expression of the enzyme converting Tinto DHT (i.e., the 5α-reductase) also occurs at the level of sciatic nerve, suggesting that the decrease of DHT levels could be due to an impairment of this enzyme. Chronic treatment for 1 month with DHT or 3α-diol increased tail nerve conduction velocity and partially counteracted the increase of thermal threshold induced by diabetes. Treatment with DHT increased tibial Na⁺,K⁺-ATPase activity and the expression of myelin protein P0 in the sciatic nerve.DHT, 3α-diol and T reversed the reduction of intra-epidermal nerve fiber density induced by diabetes. These observations indicate that T metabolites can reverse behavioral, neurophysiological, morphological and biochemical alterations induced by peripheral diabetic neuropathy. I. Roglio, R. Bianchi: These authors contributed equally to this study. Received 4 January 2007; received after revision 13 February 2007; accepted 27 March 2007     

Zinc binding to peptide analogs of the structural zinc site in alcohol dehydrogenase: Implications for an entatic state

Zinc binding to the peptide replica and analogs to residues 93–115 of horse liver alcohol dehydrogenase (ADH) was examined by competition of the peptides and the chromophoric chelator 4-(2- pyridylazo)resorcinol for zinc and X-ray absorption fine structure analysis of the zinc ligands. In the enzyme, zinc is coordinated by four Cys residues. In the peptide replica, zinc is bound to three Cys and one His residue. A four-Cys zinc coordination is observed only when His is removed, leading to increased zinc stability. ADH crystal structures reveal that the ε-amino group of the conserved residue Lys323 is within H-bond distance of the backbone amide oxygens of residues 103, 105 and 108, likely stabilizing the zinc coordination in the enzyme. The peptide data thus indicate structural strain and increased energy in the zinc-binding site in the protein, characteristic of an entatic state, implying a functional nature for this zinc site. Received 3 July 2008; received after revision 11 August 2008; accepted 1 September 2008     

Zinc,copper and selenium in reproduction

Of the nine biological trace elements, zinc, copper and selenium are important in reproduction in males and females. Zinc content is high in the adult testis, and the prostate has a higher concentration of zinc than any other organ of the body. Zinc deficiency first impairs angiotensin converting enzyme (ACE) activity, and this in turn leads to depletion of testosterone and inhibition of spermatogenesis. Defects in spermatozoa are frequently observed in the zinc-deficient rat. Zinc is thought to help to extend the functional life span of the ejaculated spermatozoa. Zinc deficiency in the female can lead to such problems as impaired synthesis/secretion-of (FSH) and (LH), abnormal ovarian development, disruption of the estrous cycle, frequent abortion, a prolonged gestation period, teratogenicity, still-births, difficulty in parturition, pre-eclampsia, toxemia and low birth weights of infants. The level of testosterone in the male has been suggested to play a role in the severity of copper deficiency. Copper-deficient female rats are protected against mortality due to copper deficiency, and the protection has been suggested to be provided by estrogens, since estrogens alter the subcellular distribution of copper in the liver and increase plasma copper levels by inducing ceruloplasmin synthesis. The selenium content of male gonads increases during pubertal maturation. Selenium is localized in the mitochondrial capsule protein (MCP) of the midpiece. Maximal incorporation in MCP occurs at steps 7 and 12 of spermatogenesis and uptake dereases by step 15. Selenium deficiency in females results in infertility, abortions and retention of the placenta. The newborns from a selenium-deficient mother suffer from muscular weakness, but the concentration of selenium during pregnancy does not have any effect on the weight of the baby or length of pregnancy. The selenium requirements of a pregnant and lactating mother are increased as a result of selenium transport to the fetus via the placenta and to the infant via breast milk.     

Effect of bilateral nephrectomy on the recovery of blood pressure after acute hemorrhage in rats: role of renin-angiotensin system

The effect of bilateral nephrectomy, and administration of an inhibitor of angiotensin converting enzyme, on the recovery of arterial blood pressure after hemorrhage (loss of 1% of b.wt), was studied in male Sprague-Dawley rats. Neither manoeuver significantly affected the recovery of blood pressure within the first 10 min after hemorrhage. Thereafter, the recovery of the blood pressure was markedly suppressed. The study suggests that the initial recovery of blood pressure is unrelated to the kidneys, but the later one requires their presence and depends on the activity of the renin-angiotensin system.     

Gametes contain angiotensin converting enzyme (kininase II)

The localization of angiotensin converting enzyme (ACE) in the gonads of the normal rabbit was studied by immunofluorescence and immunoelectron microscopy. The enzyme is present in the cytoplasm of testicular spermatids and of epididymal and ejaculated spermatozoa, and on the surface of follicular and tubal oocytes. These findings support the hypothesis that ACE has a role in gamete maturation and in fertilization.     

Effect of vitamin A deficiency on the levels of glutathione and glutathione-S-transferase activity in rat lung and liver

Summary Vitamin A deficiency reduces the content of glutathione in liver and lung. Also, glutathione S-transferase activity is decreased significantly in the lung, whereas its activity is increased in the liver.     

Chemische Kopplung von Hexokinase aus Hefe an Sephadex

Summary Yeast hexokinase was coupled to Sephadex by means of cyanogen bromide. The activity of the fixed enzyme was 2% of that before coupling. The activity of the noncoupled part of the enzyme was also decreased to the same degree. This decrease cannot be caused by the coupling reaction itself. The Michaelis-constants and the pH-activity curve of the coupled enzyme do not differ significantly from that of the free enzyme.     

Medium- and short-chain dehydrogenase/reductase gene and protein families

Zinc plays an important role in the structure and function of many enzymes, including alcohol dehydrogenases (ADHs) of the MDR type (mediumchain dehydrogenases/reductases). Active site zinc participates in catalytic events, and structural site zinc maintains structural stability. MDR-types of ADHs have both of these zinc sites but with some variation in ligands and spacing. The catalytic zinc sites involve three residues with different spacings from two separate protein segments, while the structural zinc sites involve four residues and cover a local segment of the protein chain (Cys97-Cys111 in horse liver class I ADH). This review summarizes properties of both ADH zinc sites, and relates them to zinc sites of proteins in general. In addition, it highlights a separate study of zinc binding peptide variants of the horse liver ADH structural zinc site. The results show that zinc coordination of the free peptide differs markedly from that of the enzyme (one His / three Cys versus four Cys), suggesting that the protein zinc site is in an energetically strained conformation relative to that of the peptide. This finding is a characteristic of an entatic state, implying a functional nature for this zinc site.     

The role of zinc in the activation of the enzyme cellulase in termites

Summary Chemical analysis had revealed an exceptionally high amout of zinc in the worker bodies of termites. Further investigation of the digestion of cellulose in vitro demonstrated that zinc functions as activator of the enzyme cellulase.     

Changes of X-prolyl dipeptidyl-aminopeptidase activity in developing rat brain.

We found X-prolyl dipeptidyl-aminopeptidase activity in rat brain and examined the developmental changes at various ages. The total enzyme activity per brain increased until 4 weeks of age, and then decreased during maturation. Specific activity in young rat brain was higher than that in adult rat brain. The properties of the brain enzyme were different from those of pituitary and other tissues.     

Changes of X-prolyl dipeptidyl-aminopeptidase activity in developing rat brain

Summary We found X-prolyl dipeptidyl-aminopeptidase activity in rat brain and examined the developmental changes at various ages. The total enzyme activity per brain increased until 4 weeks of age, and then decreased during maturation. Specific activity in young rat brain was higher than that in adult rat brain. The properties of the brain enzyme were different from those of pituitary and other tissues.     

Metabolic implications in the elevation of serum activity of intestinal alkaline phosphatase in chronic renal failure

The activity of intestinal isoenzyme of serum alkaline phosphatase was evaluated in 21 non-dialyzed patients with advanced renal failure and in 52 patients on regular hemodialysis. In patients without hepatopathy, a significant inverse correlation was found between the enzyme activity and serum calcium levels. Hepatopathy was the most significant variable influencing the enzyme activity in patients on dialysis. Secondary hyperparathyroidism and a decreased rate in enzyme elimination should be assessed for the above-normal activities of intestinal ALP in serum in chronic renal failure.     

Metabolic implications in the elevation of serum activity of intestinal alkaline phosphatase in chronic renal failure

Summary The activity of intestinal isoenzyme of serum alkaline phosphatase was evaluated in 21 non-dialyzed patients with advanced renal failure and in 52 patients on regular hemodialysis. In patients without hepatopathy, a significant inverse correlation was found between the enzyme activity and serum calcium levels. Hepatopathy was the most significant variable influencing the enzyme activity in patients on dialysis. Secondary hyperparathyroidism and a decreased rate in enzyme elimination should be assessed for the above-normal activities of intestinal ALP in serum in chronic renal failure.     

Metabolic implications in the elevation of serum activity of intestinal alkaline phosphatase in chronic renal failure

Summary The activity of intestinal isoenzyme of serum alkaline phosphatase was evaluated in 21 non-dialyzed patients with advanced renal failure and in 52 patients on regular hemodialysis. In patients without hepatopathy, a significant inverse correlation was found between the enzyme activity and serum calcium levels. Hepatopathy was the most significant variable influencing the enzyme activity in patients on dialysis. Secondary hyperparathyroidism and a decreased rate in enzyme elimination should be assessed for the above-normal activities of intestinal ALP in serum in chronic renal failure.     

Metabolic implications in the elevation of serum activity of intestinal alkaline phosphatase in chronic renal failure

The activity of intestinal isoenzyme of serum alkaline phosphatase was evaluated in 21 non-dialyzed patients with advanced renal failure and in 52 patients on regular hemodialysis. In patients without hepatopathy, a significant inverse correlation was found between the enzyme activity and serum calcium levels. Hepatopathy was the most significant variable influencing the enzyme activity in patients on dialysis. Secondary hyperparathyroidism and a decreased rate in enzyme elimination should be assessed for the above-normal activities of intestinal ALP in serum in chronic renal failure.     

Serum thyrosinase in human lung carcinoma.

Compared to normal humans, lung carcinoma patients show increased tyrosinase activity. 7 serum enzymic fractions or carriers were present in the diseased state. Further, serum tyrosinase inhibitory factors generally were decreased in lung carcinoma patients compared to normal individuals.     

Deficiency of kallikrein-like enzyme activities in cerebral tissue of patients with Alzheimer's disease.

We examined the changes in the intracerebral activities, at the time of postmortem autopsy, in patients with Alzheimer's disease. When compared with the control group, the activity of kallikrein-like enzyme was significantly decreased, while prolyl endopeptidase activity increased, in the patients group. Aprotinin inhibited 50% of the activity of the former enzyme at 2 x 10(-7) M. Taken together with the results of a multivariate study, the above findings may indicate that intracerebral kallikrein deficiency plays an important role in the pathogenesis of Alzheimer's disease.