This thesis is focused on bioelements for biological electric power sources,specifically, on blue copper proteins with and without an intrinsic biocatalyticactivity, i.e. ability to reduce oxygen directly to water. These proteins, viz. differentlaccases, ceruloplasmin, and rusticyanin, were characterised in detailand employed for the construction of both self-charging and conventional biosupercapacitors.First, similarities and particularities of oxygen electroreductionvs. bioelectroreduction were reviewed. Moreover, being a promising candidatefor the construction of autotolerant implantable biocathodes, the electrochemistryof human ceruloplasmin was revisited. For the first time, a clearbioelectrocatalytic reduction of oxygen on ceruloplasmin modified electrodeswas shown. Second, computational design combined with directed evolutionresulted in a high redox potential mutated laccase, GreeDo, with increased redoxpotential of the T1 site, increased activity towards high redox potentialmediators, as well as enhanced stability. Third, GreeDo was electrochemicallycharacterised in detail. The mutant exhibited higher open circuit potentialvalues and onset potentials for oxygen bioelectroreduction compared to the parental laccase, OB-1. Moreover, the operational stability of GreeDo modifiedgraphite electrodes was found to be more than 2 h in a decidedly acidicelectrolyte, in agreement with the extended operational and storage stabilitiesof the enzyme in acidic solutions. Fourth, multi-cell single-electrolyte glucose/oxygen biodevices with adjustable open-circuit and operating voltages,which are independent on the difference in equilibrium redox potentials of thetwo redox couples, gluconolactone/glucose and oxygen/water, viz. 1.18 V, butdependent on the number of half-cells in the biodevice construction, were designedand tested. The biodevices were made from tubular graphite electrodeswith electropolymerised poly(3,4-ethylenedioxythiophene) modified withTrametes hirsuta laccase and Neurospora crassa cellobiose dehydrogenase as the cathodic and anodic biocatalysts, respectively. Due to the interplay betweenfaradaic and non-faradaic electrochemical processes, as well as betweenionic and electronic conductivities, the open-circuit voltage of the self-chargedbiodevice is extraordinarily high, reaching 3 V, when seven biosupercapacitorsoperating in a common electrolyte were connected in series. Moreover,glucose/oxygen biodevices could be externally discharged at an operatingvoltage exceeding the maximal limiting open-circuit value of 1.24 V for thecomplete glucose oxidation. Last but not least, a conventional biosupercapacitor,i.e. a biodevice lacking self-charging ability, was composed of Acidithiobacillusferrooxidans rusticyanin modified gold electrodes. The complete biodevicesas well as separate electrodes were thoroughly characterised electrochemically.The symmetrical biosupercapacitor based on two identical goldelectrodes modified with rusticyanin is able to capacitively store electricityand deliver electric power, accumulated mostly in the form of biopseudocapacitance,when charged and discharged externally.