Saposin B Is a Human Coenzyme Q10-Binding/Transfer Protein

Coenzyme Q10 (CoQ10) is essential for ATP production in the mitochondria, and is an important antioxidant in every biomembrane and lipoprotein. Due to its hydrophobicity, a binding and transfer protein for CoQ10 is plausible, but none have yet been isolated and characterized. Here we purified a CoQ10-binding protein from human urine and identified it to be saposin B, a housekeeping protein necessary for sphingolipid hydrolysis in lysosomes. We confirmed that cellular saposin B binds CoQ10 in human sperm and the hepatoma cell line HepG2 by using saposin B monoclonal antibody. The molar ratios of CoQ10 to saposin B were estimated to be 0.22 in urine, 0.003 in HepG2, and 0.12 in sperm. We then confirmed that aqueous saposin B extracts CoQ10 from hexane to form a saposin B-CoQ10 complex. Lipid binding affinity to saposin B decreased in the following order: CoQ10>CoQ9>CoQ7>>α-tocopherol>>cholesterol (no binding). The CoQ10-binding affinity to saposin B increased with pH, with maximal binding seen at pH 7.4. On the other hand, the CoQ10-donating activity of the saposin B-CoQ10 complex to erythrocyte ghost membranes increased with decreasing pH. These results suggest that saposin B binds and transports CoQ10 in human cells

Fitness of optimal utilization in semelparous species.

<p>We calculate the value of the fitness of semelparous species with respect to between zero and 1. The vertical dashed line represents the boundary between specialists and generalists as given by Eq.(77). The fitness is always a monotonically increasing function of in the persistent region of the species (). It is remarkable that a large causes individuals to favor risk and increase their fitness. This figure shows the optimal resource utilization actually having advantages over specialists of each of the resources. Parameters are the same as in Fig. 2.</p

Semelparous optimal utilization for each .

<p>This figure shows the semelparous optimal resource utilization, Eq.(76), depending on . Two distinct types of feeding habitat exist. A small or intermediate value of makes the species a generalist: the larger the value of , the more the species favors risk and becomes specialist. Parameters are , , , , and .</p

A resource utilization problem.

<p>This figure illustrates how a fish wavers in its choice. represents high risk but high expected growth rate, while both quantities are low in . These resources fluctuate independently of each other. In other words, the two resources provide individuals with different internal stochasticities. The fish should optimally choose the best utilization of both resources.</p

Transition of the .

<p>This figure shows changes in the with respect to . The of the fittest species increases as increases; however, it decreases when reaches the RHS of Eq.(77), which means that the growth strategy changes from the conservation of the to a hasty alternation of generation time. Utilizing usually, the of the fittest is higher than that of . We simulate the under the same parameters as in Fig. 4. To show the proportional connection between and the , we change the variable () and simulate it within (0, 3.5) because is in inverse proportion to . Parameters are the same as in Fig. 4.</p