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Biomedical subjects

G Greco

Publications and source records attributed to G Greco.

At least 163 records · Page 9Linked to original sources
PubMed1981

Preliminary observations on the heart of the haemoglobinless Antarctic fish Champsocephalus gunnari, Lönnberg.

The heart of the haemoglobinless and myoglobinless "icefish" Champsocephalus gunnari shows interesting morphometric and histological features. The relative heart weight in two animals (body weights 479.2 and 481.0) was significantly greater than in other sea-water teleosts and corresponds to values found in small mammals (with the exception of tuna). The histological features of both the ventricular myocardium and the bulbus arteriosus as well as the unique appearance of the parietal pericardium indicate important adaptations in the circulatory functions of this animal.

Animals↗
PubMed1980

Myoglobin in the electric organ of torpedo.

The myoglobin content of the electric organ of Torpedo marmorata and Torpedo ocellata has been determined. It has been found that the chromoprotein concentration of this tissue is 70-80% as compared to that of red myotomal musculature while it is about twice that of white muscle. This result is discussed in relation to the muscular nature of the electric organ and its very specialized function.

Animals↗
PubMed1980

Myoglobin in the heart ventricle of tuna and other fishes.

The myoglobin content in the hearts of several fishes is positively correlated with the ecological physiology of the species. In the tuna heart, where the highest myoglobin values are found, the logarithmic relationship between myoglobin content and body weight is reported.

Animals↗
PubMed1980

Enzyme immobilization by means of ultrafiltration techniques.

Unstirred, plane membrane, ultrafiltration cells have been used as enzymatic reactor units. Because of the concentration polarization phenomena which take place in the system, at steady-state the enzyme is confined (dynamically immobilized) within an extremely narrow region upstream the ultrafiltration membrane. Correspondingly its concentration attains fairly high values. Kinetic studies have been therefore performed under quite unusual experimental conditions in order to better approximate local enzyme concentration levels in immobilized enzyme systems. Studies have been also carried out on the kinetics of enzyme deactivation in the continuous presence of substrate and reaction products. Once the enzyme concentration profile is completely developed, further injection into the system of suitable amounts of an inert proteic macromolecule (albumin polymers) gives rise to the formation of a gel layer onto the ultrafiltration membrane within which the enzyme is entrapped (statically immobilized). The effect of this immobilization technique has been studied as far as the kinetics of the main reaction, the substrate mass transfer resistances and the enzyme stability are concerned. The rejective properties of such gel layers towards enzymatic molecules have been exploited in producing multilayer, multi-enzymatic reactors.

Enzymes, Immobilized↗
PubMed1979

Kinetic behaviour of acid phosphatase-albumin co-polymers in homogeneous phase and under gel-immobilized conditions.

1. An analysis of the kinetic behaviour of immobilized acid phosphatase (EC 3.1.3.2) layers, gelled on the active surface of an ultrafiltration membrane, was carried out. 2. Two possible forms of such immobilized-enzyme systems were dealt with, namely enzyme-polyalbumin co-gelation through an ultrafiltration process, and enzyme co-polymerization to the same albumin polymers and subsequent gelation. 3. A preliminary analysis was also performed on both the corresponding homogeneous-phase (soluble systems to provide reference kinetics. 4. The main conclusions drawn are: (i) the enzyme-albumin co-polymers show a decrease in specific activity compared with the corresponding free enzyme in both soluble and immobilized forms; (ii) in the homogeneous phase a slight increase in the apparent Michaelis constant was measured for the co-polymerized enzyme compared with the free one, which suggests a decrease in affinity towards substrate; (iii) the activation energy in the immobilized phase is halved, compared with that in the homogeneous phase, which indicates that the combined mass-transfer/reaction step is rate-controlling.

Acid Phosphatase↗
PubMed1979

Theoretical and experimental analysis of a soluble enzyme membrane reactor.

Recently enzyme immobilization techniques have been proposed that are mainly founded on the formation of an enzyme-gel layer onto the active surface of an ultrafiltration membrane within an unstirred ultrafiltration cell. If the membrane molecular-weight cutoff is less than the enzyme molecular weight and hence such as to completely prevent enzyme permeation (once the enzyme solution has been charged into the test cell and pressure applied to the system), a time progressive increase in enzyme concentration takes place at the upstream membrane surface that can eventually lead to gelation and hence to enzyme immobilization. However, depending on the total enzyme amount fed, the maximum enzyme concentration achieved in the unsteady state could be less than the gelation level. In this situation, no immobilization occurs and the enzyme still remains in the soluble form although it is practically confined within a limited region immediately upstream the membrane and at fairly high concentrations. In this paper, the experimental conditions that allow gelling to occur are discussed together with a theoretical analysis of the soluble enzyme membrane reactor which is obtained when no gelling takes place. Such a system could be usefully employed in performing kinetic analyses at high enzyme concentration levels that are still in the soluble form.

Enzymes↗
PubMed1976

[Biological effects of radiomimetic compounds: quantitative studies of changes in the urinary excretion of creatine and creatinine in rats treated with HN-2].

Urinary creatine and creatinine excretion in rats treated by HN-2 ("bb'-dichlorodiethyl-N-methylamine") has been studied as function of dose and time from administration. Experimental results obtained in treated animals show an increased urinary excretion for creatine and decreased urinary excretion for creatinine. The variations are correctly related with the dose. Observed modifications are compared with the informations about urinary creatine and creatinine excretion after ionizing radiations exposure. Within research bounds, experimental results let to regard studied compounds as a possible biological dose indicators in the HN-2 intoxication.

Animals↗
PubMedDate not supplied

Augmentation of the affinity of HLA class I-binding peptides lacking primary anchor residues by manipulation of the secondary anchor residues.

A direct binding assay has been used to investigate the effect of the secondary anchor residues on peptide binding to class I proteins of the major histocompatibility complex. Based on predictions from a previous chemometric approach, synthetic peptide analogues containing unnatural amino acids were synthesized and tested for B*2705 binding. Hydrophobic unnatural amino acids such as alpha-naphthyl- and cyclohexyl-alanine were found to be excellent substituents in the P3 secondary anchor position giving peptides with very high B*2705-binding affinity. The binding to B*2705 of peptides optimized for their secondary anchor residues, but lacking one of the P2 or P9 primary anchor residues was also investigated. Most such peptides did not bind, but one peptide, lacking the P2 Arg residue generally considered essential for binding to all B27 subtypes, was found to bind quite strongly. These findings demonstrate that peptide binding to class I proteins is due to a combination of all the anchor residues, which may be occupied also by unnatural amino acids-a necessary step towards the development of peptidic or non-peptidic antagonists for immunomodulation.

Amino Acid Sequence↗
PubMedDate not supplied

Association between retinopathy and impaired peripheral arterial circulation in insulin-dependent diabetic patients.

This study was undertaken to investigate whether, in insulin-dependent diabetic patients, an association exists between microangiopathy (evaluated as retinopathy) and macroangiopathy (evaluated as impaired arterial circulation of the lower limbs). A total of 38 diabetic outpatients with either background (n = 25) or proliferative (n = 13) retinopathy, plus 18 diabetic outpatients of similar age (46.8 +/- 13.4 vs. 43.0 +/- 11.0 yrs) and duration of diabetes (16.8 +/- 5.8 vs. 14.8 +/- 15.1 yrs) without retinopathy were studied. Retinopathy was defined according to fluorescein angiography. The arterial circulation of the lower limbs was evaluated by the ankle/arm systolic pressure index with ultrasonic Doppler end-point detection and echo-Doppler examination of the pelvic vessels. The ankle/arm index was significantly lower in diabetic patients with retinopathy (0.98 +/- 0.16 vs. 1.12 +/- 0.11, p less than 0.002) and the percentage of persons with definitely impaired arterial circulation of the legs (ankle/arm systolic blood pressure less than 0.95) was significantly higher in this group (36.8% vs. 5.5%, p = 0.038). Of 14 patients with retinopathy and peripheral arterial disease, only three (21%) had detectable stenoses of the pelvic vessels. The overall profile of cardiovascular risk factors was similar in the two groups. The multivariate analysis indicated that retinopathy was the best correlate of impaired peripheral arterial circulation. In conclusion, in our study population, an association between retinopathy and impaired peripheral arterial circulation of the legs existed independently of major cardiovascular risk factors.

Adult↗