Molecular-sieve chromatography

Analytical exclusion chromatography

This review summarizes the development of exclusion chromatography, also termed gel filtration, molecular-sieve chromatography and gel permeation chromatography, for the quantitative characterization of solutes and solute interactions. As well as affording a means of determining molecular mass and molecular mass distribution, the technique offers a convenient way of characterizing solute self-association and solute-ligand interactions in terms of reaction stoichiometry and equilibrium constant. The availability of molecular-sieve media with different selective porosities ensures that very little restriction is imposed on the size of solute amenable to study. Furthermore, access to a diverse array of assay procedures for monitoring the column eluate endows analytical exclusion chromatography with far greater flexibility than other techniques from the viewpoint of solute concentration range that can be examined. In addition to its widely recognized prowess as a means of solute separation and purification, exclusion chromatography thus also possesses considerable potential for investigating the functional roles of the purified solutes.

Fat digestion in the newborn. Characterization of lipase in gastric aspirates of premature and term infants

We have measured lipolytic activity in gastric aspirates obtained at birth in a group of 142 infants. The infants ranged in gestational age from 26 to 41 wk. Lipolytic activity, measured by the hydrolysis of long chain triglyceride ([tri-(3)H]oleate), and expressed as nanomoles FFA per milliliter gastric aspirate per minute was 333+/-66 in 55 small premature infants (gestational age 26-34 wk and body wt 750-2,000 g) and 558+/-45 in a group of 87 larger infants (gestational age 35-41 wk and body wt 2,020-4,000 g). No activity was detected in seven infants with an unusually low pH in the gastric aspirate, 2.88+/-0.44 (compared with a mean pH level of 5.59+/-0.22 in the other 135 infants). Attempts to characterize this lipase showed that it has a molecular weight of 44-48,000, pH optimum of 3.0-5.0, that FFA acceptors (albumin) stimulate activity, whereas bile salts, taurocholate and glycocholate, cause marked inhibition at concentration >3 mM. Our survey shows that enzyme activity is present as early as 26 wk of gestation, increases with gestational age, and has the same characteristics throughout gestation. The data show that the lipase in gastric aspirates differs from pancreatic lipase, but closely resembles human and rat lingual lipase. Because the lipase has a low pH optimum and does not require bile salts, it can act in the stomach where it initiates the hydrolysis of dietary fat. We suggest that intragastric lipolysis is probably of major importance in the newborn and especially in the premature infant where it compensates not only for low pancreatic lipase, but in addition, helps to overcome the temporary bile salt deficiency through the formation of amphiphilic reaction products.

A circulatory collagenase inhibitor

There is an increased production of collagenase from explants of rabbit colon postoperatively. The enhanced reaction is not confined to the site of injury but occurs throughout the gastro-intestinal tract, suggesting that the healing process is not purely under local control. This is not the result of increased endogenous steroid production, for injection of 10 mg. cortisone acetate into rabbits for 2 or 3 days produces no alteration in bursting pressure of the colon, no decreased collagen content of the colon or skin, or increased production of collagenase.

Addition of serum significantly inhibits the collagen-collagenase reaction of tissue explants. This inhibitory effect has been demonstrated by protein fractionation methods to be due to an alpha-globulin of high molecular weight. Adult and foetal serum from several mammals all contain an alpha-globulin inhibitor to collagenase. Following injury, collagen lysis occurs as a result of increased collagenase activity. This is associated with a decrease in circulating inhibitor.

Studies on histoplasmosis IV. Elution characteristics of the histo-inhibitory factor (HIF)

The histo-inhibitory factor (HIF) derived from homogenates of liver or kidney from hamsters infected withHistoplasma capsulatum has been fractionated by column chromatography. It shows maximum absorption at 280 mµ, has a molecular weight of 142,000 and can be eluted from DEAE-cellulose or DEAE-Sephadex A—50 with 0.02 M phosphate — 4 M sodium chloride (1 : 1)

HIF can be eluted fromHistoplasma yeast cells at pH 10.0, thus a greater number of positive cultures from chronic histoplasmosis could be expected to result from pretreatment of clinical specimens in glycine buffer pH 10.0 prior to culture.