I remember back in high school ( 98 ) it was said that creatine lowered sperm count, or some shit like that. Here I am almost 10 years later, married, and lots of sex, and still no kids.( not a bad thing ), so there might be some truth to that after all, because I should have fathered my own race by now.
The opposite is true.
The enzyme creatine kinase (CK), catalyzing the reversible transfer of the N-phosphoryl group from phosphocreatine (PCr) to ADP to regenerate ATP, plays a key role in the energy homeostasis of cells with intermittently high, fluctuating energy requirements, e.g. skeletal and cardiac muscle, neurons, photoreceptors, spermatozoa and electrocytes. Cytosolic CK isoenzyme(s) (MM-, MB- and BB-CK) are always co-expressed in a tissue-specific fashion together with a mitochondrial isoform. Using biochemical fractionation and in situ localization, one was able to show that the CK isoenzymes, earlier considered to be strictly soluble, are in fact compartmentalized subcellularly and coupled functionally and/or structurally either to sites of energy production (glycolysis and mitochondria) or energy consumption (cellular ATPases, such as the acto-myosin ATPase and SR-Ca2+-ATPase). Thus they form an intricate, highly regulated energy distribution network, the so-called PCr-circuit or PCr-shuttle (Figure 1, for review see [1] and the special volumes of Mol. Cell Biochem. 133/134, 1994, and 184, 1998).
This non-equilibrium energy transport model has been challenged, based upon global 31P-NMR experiments, measuring CK-mediated flux in muscles at different work-loads [2,3]. The conclusions reached by these authors were i) that the CK system is in equilibrium with the substrates, behaving like a solution of well-mixed enzymes, ii) that effects of compartmentation were negligible with respect to total cellular bioenergetics and iii) that thermodynamic characteristics of the cytosol could be predicted as if the CK metabolites were freely mixing in solution. However, based on the organizational principles of sarcomeric muscle, as well as on our findings concerning the highly structured subcellular CK-compartments, this interpretation seemed rather unlikely and thus has been questionned [4]. In support of this, 31P-NMR CK-flux measurements with transgenic mice showing graded reductions of MM-CK expression in their muscles, revealed a strikingly unexpected, "anomalous" CK-flux behaviour [5]. These results indicate that some flux through CK, presumably bound CK, and possibly also some PCr and/or ATP, are NMR-invisible or otherwise not amenable to this analysis [4,6]. In the meantime, more evidence from NMR-measurements [7,8,9,10], as well as from recent in vivo 14[C]Cr-tracer studies [11], is accumulating in favour of compartmentation of the CK system and for the existence of different pools of CK substrates. As a matter of fact, it has now become clear that in muscle, Cr and PCr molecules do not tumble freely, but display partial orientational ordering, which is in contrast to what is expected for small molecules dissolved in water [7].
Furthermore, 31P-NMR saturation transfer experiments with sea-urchin spermatozoa show that the CK-flux increases by a factor of 10-20 upon sperm activation [12]. These specialized sperm cells derive their energy for motility entirely from fatty oxidation within the single large mitochondrion located just behind the sperm head, from where PCr is diffusing along the 50 µm long sperm tail to fuel the dynein/tubulin ATPase. It is obvious that in these polar, elongated cells, the diffusional limitation of ADP is the key limiting factor with respect to high-energy phosphate provision [13]. Also in support of the PCr-shuttle model, the calculated diffusional flux of ADP in these sperm cells is by 2 and 3 orders of magnitude smaller than those of ATP and PCr, respectively [13].In conclusion, it becomes obvious that calculations of free cellular [ADP] by using global [ATP] and [PCr], determined by in vivo 31P-NMR, together with the CK equilibrium constant, may be valid only in certain limited cases, e.g. in fast twitch glycolytic white muscle fibres, where the buffer function of CK by far prevails the transport function and where the flux through the CK reaction at rest and during high work load are higher by a factor of 100 and 20, respectively, than the total cellular ATPase turnover at these respective states. In cases where the transport function of the CK prevails, e.g. oxidative tissues or in polar cells (sea urchin sperms) with high concentrations of Mi-CK, local [ADP] and [ATP] levels, e.g. in the mitochondrial intermembrane space or near CK-ATPase complexes, may differ by orders of magnitude compared to the bulk concentrations calculated from the CK equilibrium constant. Considering the complications of subcellular compartmentation of CK isoenzymes in a cell, where after activation, some CK will work in the forward and some in the reverse direction, the interpretation of global CK flux measurements may also represent a rather difficult endeavour.