The characterization of the hexokinases in several tissues of the calf eye

Several tissues from the calf eye were studied so as to determine the characteristics of the hexokinases in each tissue. The corneal stroma, sclera, and vitreous body are devoid of measurable hexokinase activity. The tissue specific activities decrease in the following order: retina, ciliary body, corneal endothelium, lens capsule-epithelium, corneal epithelium, and lens cortex-nucleus. Each tissue possesses Types I and II hexokinase in varying proportions in the soluble and insoluble fractions; latent hexokinase is Type I in all tissues except the retina in which both Types I and II are found in the latent fraction. No hexokinase Type IIa, III, or IV is found in any ocular tissue. Michaelis constants for glucose and MgATP= are similar to those found in extraocular tissues. Except for retinal hexokinase, ocular hexokinases are quite similar to extraocular hexokinases. The activity of retinal hexokinase varies greatly and abruptly with time and with change in buffer composition; in the absence of Na2EDTA, glucose, and -SH compounds, there is a rapid deactivation of hexokinase and a shift of the soluble to the insoluble form. The relevance of these findings to glycolysis in each tissue is discussed.