Myosin: Biosynthesis, Classes and Function opens with a discussion on class I myosins, the most varied members of the myosin superfamily and a remarkable group of molecular motor proteins that move actin filaments and produce force. Class I myosin molecules have various physiological roles including maintenance of normal intestinal brush border structure, glucose homeostasis, glomerular filtration, immune function, and tumor promotion and suppression, and new studies are revealing that mutations may lead to diseases including cancer and kidney disease. Thus, the authors review the structure and function of the eight myosin-I isoforms (Myo1a-Myo1h) that are expressed in mammals. Next, the book discusses muscle contractile function and its association with the activity of the protein complex actomyosin, in which myosin exhibits enzyme activity, namely the ability to hydrolyze ATP. The demonstrated ability of calix[4]arenes C-97, C-99, C-90 and thiacalix[4]arenes C-798 and C-800 can be used for further research aimed at the use of these compounds as novel pharmacological agents able to efficiently restore normal contractile function of myometrium by inhibition or activation of this function, or the eliminating negative effects of heavy metal cations. Following this, the authors present the results of their experiments on studying the effects of different isotopes of magnesium and zinc on the enzymatic activity of myosin, namely the catalytic subfragment-1 of myosin, isolated from myometrium muscle. It has been revealed that the rate of the enzymatic ATP hydrolysis is 2–2.5 times higher in the reaction media enriched with the magnetic isotope, 25Mg, as compared to the activity of the same enzyme in the reaction media enriched with the nonmagnetic isotopes, 24Mg or 26Mg or MgCl2 of natural isotope abundance. Continuing, precipitation/extraction methods and MALDI TOF/TOF mass spectrometry were used in order to and identify, for the first time, a protein with the molecular mass of 48 kDa as a fragment of human unconventional myosin 1c isoform b in a blood serum of multiple sclerosis patients. Western-blot analysis using commercial monospecific anti-human Myo1c antibodies has shown that the molecular mass of this protein obtained from a blood serum of different human sources varied in between 46-48 kDa. Thus, the authors name the 46-48 kDa proteins revealed in a blood serum as a short form of the human unconventional myosin 1c (sMyo 1C).