Quantitative analysis of tubulin and microtubule compartments in isolated rat hepatocytes

A combined morphometric and biochemical approach has been used to identify and quantitate microtubules and tubulin in isolated hepatocytes. The total soluble pool of microtubule protein was estimated by specific high affinity binding to radiolabeled colchicine. Scatchard analysis of the data identified two populations of binding sites: high affinity-low capacity sites resembling tubulin and low affinity-high capacity sites believed to represent nonspecific colchicine-binding sites. Data from these studies indicate that tubulin represents 1% of the soluble protein of the cell, that 9.0 X 10(-14) dimers of tubulin are present per microgram soluble hepatocyte protein, and that the average hepatocyte contains 3.1 X 10(7) tubulin dimers. Our calculations suggest that this amount of tubulin would form a microtubule 1.9 cm in length if totally assembled. However, stereological measurements indicate that the actual length of microtubules in the cytosolic compartment of the average hepatocyte is only 0.28 cm. Thus, these experiments suggest that only 15% of the available tubulin in hepatocytes of postabsorptive rats is assembled in the form of microtubules.

Structural convergence during protein evolution

Several recent protein crystallographic structure determinations have demonstrated the existence of considerable tertiary structural similarity among proteins otherwise having little similarity in either amino acid sequence or biological function. In order to assess the possibility that such proteins may have arisen through processes of divergent evolution from a common ancestor, a graphical presentation is given which correlates the pattern of allowed single base substitutions defined by the genetic code with the associated changes in the structural properties of the encoded amino acids. The results show that while a large degree of structural conservation is evident due to codon synonomy, there is, in general, little tendency for the code to be structurally conservative in the majority of the cases where codon single-base changes result in amino acid substitutions. The possible consequences of this pattern of potential amino acid substitutions are discussed in relation to protein evolutionary processes.

Perinatal care of low-risk mothers and infants. Early discharge with home care

A family-centered perinatal-care program featuring collaboration by nurse practitioners, obstetricians, pediatricians, and paramedical personnel was developed to enhance family participation and achieve a shorter but safe hospital stay. Discharge from the hospital was permitted as early as 12 hours after delivery. A perinatal nurse practitioner made daily home visits. The program's safety, feasibility, and acceptability to patients was studied by comparison of 44 patients so treated (study group) with 44 receiving traditional care (controls). Twenty-one study families, but no controls, went home within 24 hours. The study and control groups had no significant differences or trends in numbers of types of morbidity during hospitalization or the six-week post-partum period. The expense of the program is approximately equaled by hospital costs saved through early discharge. The results indicate that early discharge with home-care follow-up observation as described is safe, economically feasible, and well accepted by patients.

Uterine response to nerve stimulation; relation to hormonal status and catecholamines

Immature Dutch rabbits were treated as follows: group 1, 70 µg estradiol-17ß every other day for 4 days; group 2, 70 µg estradiol-17ß every other day for 4 days, then 5 mg progesterone daily for 5 days; group 3, untreated controls. Uterine muscles with their hypogastric nerves attached were isolated, and the responses of the uterus to hypogastric nerve stimulation were recorded. Nerve stimulation (5–50 pulses/sec) contracted uteri from untreated and estrogen-treated rabbits. Nerve stimulation inhibited the spontaneous contractions of estrogen + progesterone-treated animals. These effects were unchanged by atropine or hexamethonium but were abolished by the adrenergic blocking agents phentolamine (estrogen-treated uteri) and propranolol (estrogen + progesterone-treated uteri). Uterine catecholamine content was unaltered by hormonal treatment. Pretreatment with reserpine greatly diminished uterine catecholamine content as well as the response to nerve stimulation in all animals. The hypogastric nerves therefore contain predominantly postganglionic adrenergic fibers, and the effects of their stimulation on uterine activity depend on the hormonal status of the myometrium.