Repercussions of the COVID-19 pandemic on athletes: a cross-sectional study

The COVID-19 pandemic has presented significant challenges and implications for the sports community. Thus, this study aimed to describe the prevalence of COVID-19 in Brazilian athletes and identify the epidemiological, clinical, athletic, life and health factors associated with the disease in these individuals. A cross-sectional study was performed involving 414 athletes from 22 different sports using an online questionnaire from August to November 2020. The association between the athletes’ characteristics and COVID-19 was evaluated using a logistic regression model. The prevalence of COVID-19 was 8.5%, although only 40% of athletes reported having been tested. Being under 27 years of age (3-fold), having children (~5-fold), having a teammate test positive for COVID-19 (2.5-fold), and smoking (14-fold) were associated with a possible higher risk of disease. Almost 20% of athletes self-reported musculoskeletal injuries during the period of the pandemic that was studied. Athletes with a university education (P = 0.02), a profession other than sports (P < 0.001), those from a low-income family (P = 0.01), and public health system users (P = 0.04) were significantly less frequently tested for COVID-19, whereas international competitors, athletes who received a wage, and athletes who had a teammate who tested positive for COVID-19 were 2-, 3-, and 15-fold more likely to be tested for COVID-19, respectively. Approximately 26% of the athletes who tested negative or were untested reported more than three characteristic COVID-19 symptoms, and 11% of athletes who tested positive for COVID-19 were asymptomatic. The identification of modifiable (have children, smoking, and teammates positively tested) and non-modifiable (age under 27 years) factors related to COVID-19 in athletes can contribute to implementing surveillance programmes to decrease the incidence of COVID-19 in athletes and its negative impacts in sports.     

Oligomeric enzymes in the C4 pathway of photosynthesis

This review deals with the factors controlling the aggregation-state of several enzymes involved in C₄ photosynthesis, namely phosphoenolpyruvate carboxylase, NAD-and NADP-malic enzyme, NADP-malic dehydrogenase and pyruvate, phosphate dikinase and its regulatory protein. All of these enzymes are oligomeric and have been shown to undergo changes in their quaternary structure in vitro under different conditions. The activity changes linked to variations in aggregation-state are discussed in terms of their putative physiological role in the regulation of C₄ metabolism.Abbreviations P-enolpyruvate phosphoenolpyruvate - NAD-ME NAD-dependent malic enzyme - NADP-ME NADP-dependent malic enzyme - NADP-MDH NADP-dependent malic dehydrogenase - PPDK pyruvate, phosphate dikinase - PPDK-RP pyruvate, phosphate dikinase regulatory protein - V_max maximal velocity - K_m Michaelis constant - CAM Crassulacean acid metabolism     

NADP-malic enzyme: immunolocalization in different tissues34 plant maize and the C3 plant wheat

In situimmunolocalization and Western blot analysis of separatedcellular and subcellular fractions, were used to determine thelocalization of different isoforms of NADP-malic enzyme in bothwheat (C₃) and maize (C₄) plants. In both techniques, an affinitypurified anti-(maize 62 kDa NADP-ME) lgG from the maize greenleaf isoform also reacted with a 72 kDa protein in tissues ofC4 plants as well as C3 plants. The light- inducible 62 kDaisofomi is located in bundle sheath chioroplasts of maize leaves.In etiolated leaves and in roots of maize there is evidencefor the occurrence of a 72 kDa isoform which co-migrates on2-D (SDS and isoelectric focusing) PAGE. The 72 kDa isoformis also present in low levels in green leaves. This form mayoccur in multiple intracellular compartments; but in situ immunolocalizationexperiments and Western blot and activity assays on fractionatedprotoplasts indicate that a significant amount of this isoformoccurs in plastids. With regards to C³ plants such as wheat,a 72 kDa isoform in leaves is largely confined to the chloroplastsbased on in situ immunolocalization and Western blots and enzymeactivity assays with fractionated protoplasts. In maize, itappears that the constitutive expression pattern of a possibleC₃ ancestral gene for NADP-malic enzyme has been maintained,and a high level expression of a light-inducible isoform locatedin bundle sheath chloroplasts (62 kDa) has been acquired duringits evolution. Key words: NADP-malic enzyme, Triticum aestivum, Zea mays     

Red and Infrared Low-Level Laser Therapy Prior to Injury with or without Administration after Injury Modulate Oxidative Stress during the Muscle Repair Process

IntroductionMuscle injury is common among athletes and amateur practitioners of sports. Following an injury, the production of reactive oxygen species (ROS) occurs, which can harm healthy muscle fibers (secondary damage) and delay the repair process. Low-level laser therapy (LLLT) administered prior to or following an injury has demonstrated positive and protective effects on muscle repair, but the combination of both administration times together has not been clarified.AimTo evaluate the effect of LLLT (660 nm and 780 nm, 10 J/cm², 40 mW, 3.2 J) prior to injury with or without the administration after injury on oxidative stress during the muscle repair process.MethodsWistar rats were divided into following groups: control; muscle injury alone; LLLT 660 nm + injury; LLLT 780 nm + injury; LLLT 660 nm before and after injury; and LLLT 780 nm before and after injury. The rats were euthanized on days 1, 3 and 7 following cryoinjury of the tibialis anterior (TA) muscle, which was then removed for analysis.ResultsLipid peroxidation decreased in the 660+injury group after one day. Moreover, red and infrared LLLT employed at both administration times induced a decrease in lipid peroxidation after seven days. CAT activity was altered by LLLT in all periods evaluated, with a decrease after one day in the 780+injury+780 group and after seven days in the 780+injury group as well as an increase in the 780+injury and 780+injury+780 groups after three days. Furthermore, increases in GPx and SOD activity were found after seven days in the 780+injury+780 group.ConclusionThe administration of red and infrared laser therapy at different times positively modulates the activity of antioxidant enzymes and reduces stress markers during the muscle repair process.     

Purification of NADP-Malic Enzyme and Phosphoenolpyruvate Carboxylase from Sugar Cane Leaves

A procedure is described for the purification of phosphoenolpyruvatecarboxylase (EC 4.1.1.31 [EC] ) and NADP-dependent malic enzyme (EC1.1.1.40 [EC] ) from sugar cane leaves. Each enzyme was purified tohomogeneity as judged by sodium dodecyl sulfate-polyacrylamidegel electro-phoresis, with about 30% yield. Phosphoenolpyruvatecarboxylase was purified 54-fold. A molecular weight of 400,000and a homotetrameric structure were determined for the nativeenzyme. The purified carboxylase had a specific activity of20.0 {diaeresis}mol (mg protein)_–1 min_–1, and wasactivated by glucose-6-phosphate and inhibited by L-malate.K_m values at pH 8.0 for phosphoenolpyruvate and bicarbonatewere 0.25 and O.l0 mM, respectively. NADP-malic enzyme, 356-foldpurified, exhibited a specific activity of 71.2 {diaeresis}mol(mg protein)_–1 min_–1 and was characterized as ahomotetramer with native molecular weight of 250,000. Purifiedmalic enzyme showed an absolute specificity for NADP⁺ and requireda divalent metal ion for activity. K_m values of 0.33 and 0.008mM for L-malate and NADP⁺, respectively, were determined. Thisenzyme was inhibited by several organic acids, including ketoand amino acids; while succinate and citrate increased the enzymeactivity when assayed with 10{diaeresis}M L-malate. The effectsshown by amino acids and by citrate were dependent on pH, beinghigher at pH 8.0 than at pH 7.0. (Received October 26, 1988; Accepted February 3, 1989)     

Changes in the quaternary structure of phosphoenolpyruvate carboxylase induced by ionic strength affect its catalytic activity

Phosphoenolpyruvate carboxylase from maize leaves dissociated into dimers and/or monomers when exposed to increasing ionic strength (e.g. 200-400 mM NaCl) as indicated by gel filtration experiments. Changes in the oligomerization state were dependent on pH, time of preincubation with salt and protein concentration. A dissociation into dimers and monomers was observed at pH 8, while at pH 7 dissociation into the dimeric form only was observed. Exposure of the enzyme to higher ionic strength decreased the activity in a time-dependent manner. Turnover conditions and glucose 6-phosphate protected the carboxylase from the decay in activity, which was faster at pH 7 than at pH 8. The results suggest that changes in activity of the enzyme, following exposure to high ionic strength, are the consequence of dissociation. Tetrameric and dimeric forms of the phosphoenolpyruvate carboxylase seemingly reveal different catalytic properties. We suggest that the distinct catalytic properties of the different oligomeric species of phosphoenolpyruvate carboxylase and changes in the equilibrium between them could be the molecular basis for an effective regulation of metabolite levels by this key enzyme of C4 plants.     

Diffusible Fraction of Serum Cholesterol and Atherogenesis

CHOLESTEROL is found in the blood as a structural component of lipoproteins concerned with the transport of other lipids¹. The high resolution nuclear magnetic resonance spectra of high density serum lipoproteins are similar to that observed when lipids are dissolved in organic solvents, or dispersed in water by bile salts or detergents, or in sonicated form. The lipid component in lipoproteins is therefore probably in an extremely fluid condition². If human serum is mixed with paraffin oil, some of the cholesterol diffuses into the oil without affecting the ultraviolet absorption spectrum of serum proteins. This procedure avoids any protein denaturing action used for cholesterol extraction^3–5. It therefore seems that serum cholesterol has two fractions, one strongly bound by lipoprotein structures and the other loosely bound and diffusible in an oil phase. In this article I designate the loosely bound fraction “diffusible”.     

Carboxylation and dephosphorylation of phosphoenol-3-fluoropyruvate by maize leaf phosphoenolpyruvate carboxylase.

The analogue (Z)-phosphoenol-3-fluoropyruvate [(Z)-3-fluoro-2-(phosphono-oxy)propenoic acid] was tested as substrate of maize leaf phosphoenolpyruvate carboxylase. Studies with NaH14CO3 indicate that the analogue is carboxylated by the enzyme. However, this reaction accounts for only one-tenth of the activity measured by Pi liberation. The rest of the analogue is merely dephosphorylated. This is the first analogue for which both carboxylation and dephosphorylation have been observed.     

On the molecular mechanism of maize phosphoenolpyruvate carboxylase activation by thiol compounds

Incubation of purified phosphoenolpyruvate carboxylase from Zea mays L. leaves with dithiothreitol resulted in an almost 2-fold increase in the enzymic activity. The activated enzyme showed the same affinity for its substrates and the same sensitivity with respect to malate and oxalacetate inhibition. The activation induced by dithiothreitol was reversed by diamide, an oxidant of vicinal dithiols, suggesting that the redox state of disulfide bonds of the enzyme may be important in the expression of the maximal catalytic activity.

Titration of thiol groups before and after activation of maize phosphoenolpyruvate carboxylase by dithiothreitol shows an increase of the accessible groups from 8 to 12 suggesting that the reduction of two disulfide bonds accompanied the activation. The thiols exposed by the treatment with dithiothreitol were available to reagents in nondenatured enzyme and two of them were reoxidized to a disulfide bond by diamide. It is concluded that the mechanism of phosphoenolpyruvate carboxylase activation by dithiothreitol involves the net reduction of two disulfide bonds in the enzyme.