Relative Activity Values Research Articles

COPOLYMERS ON THE BASIS OF (p-CHLOROPHENOXYCARBONYL)-CYCLOPROPYL STYRENE WITH STYRENE AND METHYL METHACRYLATE

The radical copolymerization of (p-chlorophenoxycarbonyl)cyclopropyl styrene with styrene and methyl methacrylate has been carried out. New cyclopropane-containing copolymers have been obtained. It has been established that the synthesized copolymers due to peculiarities of their structure and polyfucntionality, namely with content of carbonyl and cyclopropane groups sensitive to UV irradiation in the macromolecule have photosensitivity. The constant values of relative activity of monomers have been determined and Q-e parameters on Alfrey and Price have been calculated. The copolymerization constants of this compound (r1) with styrene and methyl methacylate (r2), calculated on Fineman-Ross method are: r1 = 1.1 and1.05, but r2 = 0.56 and 0.48, respectively; Q and e parameters values: Q1 = 3.1 and 2.4, e1 = –1.4 and –0.8, respectively. The photochemical structuring has been investigated and it has been shown that the structuring process proceeds due to of cyclopropane ring opening and carbonyl group. The composition and structure of these copolymers have been established and their some characteristics (heat resistance, hardness, adhesive strength, water absorption) have been investigated. The structuring process has been also studied and it has been established that the synthesized copolymer has relatively high photosensitivity (50–55 cm2J-1)

NEGATIVE PHOTORESISTS ON THE BASIS OF COPOLYMERS OF 2-CHLOROMETHYL-1-(PVINYL PHENYL)CYCLOPROPANE WITH GLYCIDYL METHACRYLATE

The radical copolymerization of 2-chloromethyl-1-(p-vinyl phenyl)cyclopropane with glycidyl methacrylate is carried out. The composition and structure of the obtained copolymer are established. The constant values of relative activity of monomers are determined and Q-е parameters on Alfrey-Price are calculated. The photosensitivity of new cyclopropane and epoxy-containing photosensitive copolymers is studied. The photochemical structuring is investigated and it is established that the synthesized polymer has a photosensitivity (56 cm2/J) and can be used for creation of photosensitive material.

Sorption behavior and storage stability of microencapsulated transglutaminase by ultrasonic spray–freeze–drying

Adsorption isotherms at 25 °C and 38 °C for microencapsulated microbial transglutaminase (mTG) powder produced by ultrasonic spray–freeze–drying (USFD), conventional spray drying (CSD), and conventional freeze–drying (CFD) methods and USFD–crude (without coating materials) were obtained using the standard static gravimetric method, and experimental data were fitted to the mathematical models. The sorption isotherms exhibited type III behavior, and the Ferro–Fontán model was selected as the best fit, having an R 2 of 0.920–0.995. The sorption isotherms of mTG powder depended on temperature and drying methods. The equilibrium moisture content decreased with increasing temperature, and the monolayer moisture content of the USFD sample was lower than other microencapsulated samples (M 0 = 0.133 kg/kg dry solids for 25 °C and M 0 = 0.080 kg/kg dry solids for 38 °C from Guggenheim–Anderson–deBoer model), followed by CFD and CSD. Furthermore, the storage stability of mTG powders produced by different methods in terms of quality parameters including enzyme activity, moisture content, water activity, color, density, porosity, flowability, and caking degree value was studied in aluminum-laminated polyethylene (ALPE) pouches under storage conditions of 25 °C, 50% relative humidity (RH) for 180 days and 38 °C, 90% RH for 90 days. Inactivation kinetics, the effect of drying methods, and application of the microencapsulation process were also examined on mTG powder during the storage period. The first-order kinetic reaction was successfully applied to the relative activity values of all samples for both storage conditions. Both the drying method and application of microencapsulation showed a significant effect on enzyme activity. When comparing the drying techniques, the USFD samples were the most stable, having 816 and 465 days of half-life times for both storage conditions, respectively. Storage at 25 °C, 50% RH increased the half-life twofold compared with that of the USFD samples kept at 38 °C, 90% RH. The physical properties of mTG powder obtained either USFD, USFD–crude, CFD, or CSD showed that moisture content and wettability values increased, while caking degree and enzyme activity values decreased during storage. USFD samples had the lowest moisture content (5.48%) and Hausner ratio (1.12) and the highest relative activity (86.2%) compared with other samples after 180 days storage at 25 °C, 50% RH. When all quality characteristics and enzyme stability were considered, the USFD method was superior to others, and it was determined to be the best method for the production of microencapsulated mTG powders. mTG powders stored at 25 °C, 50% RH exhibited a longer shelf life.

Effect of Curing Temperature on Activity Index of Silica Fume

The compressive strength of the contrast mortars and test mortars at different curing temperatures at different ages were tested. Effect of curing temperature on the strength of the test mortars and the contrast mortars was analyzed. The relative activity index and absolute activity index of the silica fume were studied. The mercury porosimetry method was used to test the pore structure of mortar specimens, and the improving effect of silica fume on the pore structure of mortar specimens under different curing temperatures was analyzed. The results show that with the increase of age, the decrease of curing temperature will cause the strength of mortar specimens to slow down. At the 3d and 7d ages, with the decrease of curing temperature, the absolute activity value of silica fume gradually increases. After 7 days of age, with the decrease of curing temperature, the absolute activity of silica fume gradually decreases. With the increase of curing age, the relative activity of silica fume decreases at first and then increases at 20°C and 10°C. The relative activity value of silica fume under the maintenance of 5°C and -3°C increased first and then decreased gradually. The addition of silica fume in the concrete improved the internal pore structure of the specimen, and the effect of curing temperature on the specimen was consistent.

COPOLYMERIZATION OF (p-VINYLPHENYL)CYCLOPROPYLMETHYLCINNAMATE WITH GLYCIDILMETHACRYLATE

The radical copolymerization of (p-vinylphenyl) cyclopropylmethylcinnamate with glycidilmethacrylate has been studied. New cyclopropane- and epoxycontaining photosensitive copolymers have been prepared. The constant values of relative activity of monomers have been determined and the parameters of Q-e on Alfrey and Price have been determined. The copolymerization constants of the given compound (r 1 ) with glycidylmethacrylate (r 2 ) calculated on Fineman-Ross method are: r 1 = 1.05, r 2 = 0.4 correspondingly; the parameters values Q and e: Q 1 = 1.82, e 1 = -0.79 correspondingly. The composition and structure of this copolymer has been established. The photochemical investigations of the synthesized copolymer have been carried out. It has been established that the structuring proceeds due to cyclopropane ring opening and epoxide groups and also double bond in cinnamate fragment.

Biochemical characterization of solvent, salt, surfactant and oxidizing agent tolerant proteases from Aspergillus niger produced in different agroindustrial wastes

Abstract Proteases produced by Aspergillus niger LBA 02 under solid state fermentation using different agroindustrial wastes had their enzyme activities tested in the presence of organic solvents, NaCl, surfactants and oxidizing agents. The results showed that according to the fermentation substrate, the microorganism was able to secrete proteases with different biochemical characteristics. When wheat bran was used as the substrate, the proteases showed the highest relative activity in 50% (v/v) petroleum ether, reaching 114.3%, while the proteases produced in soybean meal and cottonseed meal presented 94.7% and 106.1%, respectively. These enzymes also presented high relative activity values in 50% (v/v) chloroform, retaining up to 85% of their initial protease activities after 3 h at 37 °C. When surfactants and oxidizing agents were tested, the proteases produced in soybean meal proved to have remarkable and the highest activity followed by the proteases produced in wheat bran and cottonseed meal. Since the protease produced in wheat bran showed considerable tolerance at high concentrations of NaCl, with relative activity of 61.1% at 15% NaCl (w/v), while the proteases produced in soybean meal and cottonseed meal retained 48.7% and 46.3% of their initial activities, respectively. This work provides an interesting approach about the modulation of biochemical properties of enzymes in response to different substrates, what can be used for obtaining proteases with specific applications.

Synthesis, Radical Copolymerization of (p-vinylphenyl)cyclopropyl chlorocinnamate with Styrene and Photosensitivity of the Prepared Copolymer

The radical copolymerization of of (p-vinylphenyl)cyclopropyl chlorocinnamate with styrene has been studied. The new cyclopropane-containing photosensitive copolymer has been prepared. The composition and structure of the synthesized copolymer have been established, the constant values of relative activity of monomers have been determined and the parameters Q-e have been calculated. The dependence of photosensitivity on composition of copolymer has been revealed.

Investigation of Photosensitivity of Copolymer with (P-Vinyl Phenyl) Cyclopropyl Methyl Cinnamate

The radical copolymerization of (p-vinyl phenyl) cyclopropyl methyl cinnamate with methyl methacrylate has been studied. New cyclopropane-containing photosensitive copolymers have been prepared. The constant values of relative activity of monomers have been determined and the parameters of Q-e on Alfrey and Price have been calculated. The copolymerization constants of this compound (r1) with methyl methacrylate (r2) calculated on Fineman-Ross method are r1 =1.05, r2 = 0.4, respectively; parameter values Q and e: Q1 =2.5, e1 = -0.9, respectively. The composition and structure of these copolymers have been established. The photochemical investigations of the synthesized copolymer have been carried out. It has been established that a structuring proceeds due to opening of cyclopropane ring and carbonyl groups and also double bond in cinnamate fragment.

Kiwano (cucumis metuliferus) bitkisindeki peroksidaz enzimleri üzerine amino asit etkisinin incelenmesi

In the study, peroxidase and ascorbate peroxidase are extracted from kiwano (Cucumis metuliferus). It is searched that the effect of 8 amino acids having acidic, basic, neutral characters (L-Histidine, L-Glutamic acid, L-Threonine, L-Lysine, L-Arginine, L-Aspartic acid, L-Proline, L-Phenylalanine) on these enzymes’ activity. By being based on 4 different concentrations of each amino acid solution, it is analyzed the impacts on enzymes seperately and calculated the % relative activity values of enzymes. According to the results, as some amino acids increase the activity of enzymes, others decreases. Moreover, it is seen that different concentrations of the same amino acid change enzyme activity.

Electrochemical and SOD activity studies of copper(II) complexes of bis(imidazol-2-yl) derivatives

Ligands containing the bis(imidazol-2-yl) moiety form very stable bis(ligand) [CuHxL2] (x=0–4) copper(II) complexes, with the coordination of four imidazole nitrogens. Moreover, in the presence of excess metal ion, a trinuclear species with an imidazolato bridge is formed in the case of some amino- and peptide derivatives of the bis(imidazol-2-yl) group (e.g. His-BIMA). The coordination mode of the copper(II) ion in these complexes could mimic the binding of the metal ion in the active centre of the CuZnSOD enzyme. In order to reinforce these assumptions, electrochemical and SOD activity studies of copper(II) complexes of three simple bis(imidazol-2-yl) ligands (BIM, BIMA and BIP) and five amino acid derivatives containing the bis(imidazol-2-yl) group (Z-Gly-BIMA, Z-Ala-BIMA, Gly-BIMA, β-Ala-BIMA and His-BIMA) were carried out. The measured redox potential values characterizing the [CuHxL2] (x=0–2) complexes of bis(imidazol-2-yl) derivatives, where the metal ion is bound through imidazole nitrogens, are around 0V, and a linear trend can be observed between the formal potential and the logarithmic value of the stability constants. It was not possible to determine the redox parameters of the polynuclear complex of His-BIMA. The SOD activity measurements of the bis(ligand) and trinuclear complexes show that the relative activity values characterizing the activity of the four imidazole coordinated bis(ligand) complexes are not so high, in agreement with their stabilities and formal potentials. The relative activity value of the imidazolato bridged [Cu3H−4L2] complex of His-BIMA is, however, higher than the ones published in the literature.

Mutations in CYP1B1 cause primary congenital glaucoma by reduction of either activity or abundance of the enzyme

Primary congenital glaucoma (PCG) is an autosomal recessive disorder caused predominantly by mutations in the CYP1B1 gene. A total of five frequent single nucleotide polymorphisms (SNPs) have been identified in the coding sequence of CYP1B1: rs10012C>G (p.R48G), rs1056827G>T (p.A119S), rs1056836C>G (p.V432L), rs1056837C>T (p.D449D), and rs1800440A>G (p.N453S). We performed a functional characterization of four common CYP1B1 variants presenting different coding SNP haplotypes (RAVDN, GSLDN, RALDS, and RALDN) and five CYP1B1 mutations reported for PCG patients: c.182G>A (p.G61E), c.608A>G (p.N203S), c.1033_1035del (p.L343del), c.241 T>A (p.Y81N), and c.685G>A (p.E229 K). Each mutation was embedded in its corresponding background SNP haplotype. The common variants revealed variation in enzymatic activity; among them, RAVDN showed the highest activity. Mutants p.G61E, p.N203S, and p.L343del each revealed a residual activity (<10%) of their respective haplotype. The microsomal CYP1B1 abundance relative to total protein also showed variation in common variants and a significant reduction in p.L343del, p.Y81N, and p.E229 K. The free energy of folding (DeltaDeltaG) values suggest that the lower stability of the mutants is one key property leading to the experimentally observed lower protein abundance. Our new measure of relative enzymatic activity (U/mg total protein), which combines activity and abundance values, was significantly lower for all five mutations compared to the corresponding background haplotype. We classified p.Y81N and p.E229 K not as mutations but as hypomorphic alleles, since their relative activity values are intermediate between bona fide mutations and the common variant with the lowest activity (RALDS). We propose that CYP1B1 mutations can act by either reducing enzymatic activity (p.G61E and p.N203S), reducing the abundance of the enzyme (p.Y81N and p.E229 K), or both (p.L343del).

A simple method for estimation of agonist activity at GPCRs: characterization of responses elicited by M2 and M3 muscarinic receptors

We investigated a parameter termed intrinsic relative activity (RAi), which provides a measure of agonist activity in functional assays. The RAi value is equivalent to the product of observed affinity and intrinsic efficacy of the agonist‐receptor‐G protein complex. To demonstrate that the validity of the RAi analysis, we measured the observed affinity and intrinsic efficacy values of selected agonists using Furchgott's method of partial receptor inactivation and compared the product of these estimates with the corresponding RAi estimate. We found good agreement between RAi and the product of affinity and efficacy in experiments on M3 muscarinic receptor stimulation of contraction of mouse ileum. Since observed affinity and efficacy are parameters inherent to the agonist‐receptor‐G protein complex, the RAi value is expected to be the same for various biological systems utilizing the same receptor‐G protein signaling pathway. We tested this hypothesis by comparing RAi values of muscarinic agonists for inhibiting the electrically paced guinea pig atrium and for inhibiting forskolin stimulated cAMP accumulation in CHO cells expressing the M2 receptor. Our results showed good agreement between the RAi estimates of selected agonists (oxotremorine‐M, oxotremorine, S‐aceclidine, arecoline, bethanechol, pilocarpine and McN‐A‐343) across the two assays.Supported by NIH grant 69829

The intrinsic relative activity of an agonist and its correlation to affinity and efficacy

We investigated a method for estimating the receptor-dependent component of agonist activity called intrinsic relative activity (RAi). This parameter is calculated from the agonist concentration-response curve, and it represents the product of observed affinity and intrinsic efficacy of an agonist expressed relative to that of a standard agonist. Consequently, RAi should be dependent mainly on the agonist-receptor-G protein interaction and unaffected by downstream signaling elements. To validate the RAi analysis, we estimated the affinities and relative efficacies of a series of agonists using Furchgott's method of partial receptor inactivation, and compared the respective product of these two parameters with the corresponding RAi estimate for each agonist. In these experiments, we explored agonist–mediated inhibition of forskolin-stimulated cyclic AMP production in Chinese hamster ovary cells stably expressing the human M2 muscarinic receptor. The log product of affinity and efficacy for the agonists, oxotremorine-M, oxotremorine and S-aceclidine, expressed relative to carbachol, were 0.782 ± 0.06, 0.641 ± 0.08 and -0.369 ± 0.05, respectively. The corresponding log RAi values were 0.653 ± 0.05, 0.748 ± 0.17 and -0.183 ± 0.07, respectively. Our results indicate that RAi is a relative measure of the product of affinity and efficacy of an agonist-receptor complex. Supported by NIH grant 69829.

TH‐D‐330A‐04: A Novel PET Respiratory Gating Algorithm to Reduce Lung Tumor Blurring Using the 4D NCAT Phantom

Purpose: Develop and validate a PET gating algorithm based on the amplitude of respiration to correct for abnormal respiratory cycles. Method and Materials: Using the 4D NCAT phantom model, 3D PET images were simulated in lung and other structures at different times within a respiratory cycle. To compare the amplitude gating algorithm with time gating, NCAT phantom was used to simulate a case with 5 different respiratory periods. We generated 6–10 frames over one respiratory cycle (corresponding to 3–5 s respiratory periods) and summed the results to mimic clinical imaging. Images were reconstructed with and without respiration motion. Comparison was performed for gated and un‐gated images, and for the new amplitude binning algorithm with the time binning algorithm by calculating the mean number of counts in the ROI. Lesion‐to‐background ratios were 2.5, 5 and 8. Lesion diameters were 6 mm, 8.5 mm, 10 mm and 20 mm. Simulated images were created using a Gaussian distributed random number generator. Blurring due to the finite PET image resolution was simulated by the convolution of each slice with a Gaussian filter with FWHM of 1.6 pixel. Results: As both the L/B ratio and lesion size decreases, image degradation due to respiration increases. The greater benefit for smaller diameter lesion and lower L/B ratio indicates a potential improvement in detecting more problematic lesions. Little improvement is gained for large lesions with high L/B ratios. But these are relatively easy to diagnose and gating is probably not necessary. Conclusion: From the study made using 4D NCAT simulation, it was observed that in each selected ROI, the relative activity values in four cases are: Ideal PET images (without respiratory motion) &gt; Amplitude Gated PET images &gt; Time Gated PET images &gt; Un‐gated PET images, here greater value means better and more accurate lesion detection.

Analysis of Allosterism in Functional Assays

The theoretical basis for analyzing the effects of an allosteric modulator on the response to an agonist is described. The effects of an allosteric modulator on the concentration-response curve to an agonist can be attributed to changes in the observed dissociation constant and intrinsic efficacy of the agonist-receptor complex. Each of these two changes can be represented by a coefficient or factor. It is possible to estimate the ratio of the coefficient of change in agonist efficacy divided by that for the agonist dissociation constant. This ratio is designated as the relative activity (RA) of the agonist in the presence of the allosteric modulator. The RA value can be estimated for each concentration of allosteric modulator by nonlinear regression analysis, regardless of the shape of the concentration-response curve. Regression analysis of the RA values against the concentration of allosteric modulator yields estimates of the dissociation constant (K(A)) of the allosteric modulator and the maximal RA value. If the concentration-response curve to the agonist obeys a logistic function and the allosteric modulator influences the maximal response, it is possible to distinguish between the maximal change in affinity from that of efficacy. If the agonist concentration-response curve obeys a logistic equation with a Hill slope of 1, the RA values can be estimated easily from the agonist EC(50) and E(max) values. This analysis illustrates the utility of the RA value in quantifying allosteric effects.

TheBriggs-Rauscher Reaction as a Test to Measure the Activity of Antioxidants

A new method for monitoring the relative activity of antioxidants is presented, and its advantages and limits are discussed. The method is based on the previously reported inhibitory effects of free-radical scavengers on the oscillations of the Briggs-Rauscher reaction. The effect consists of an immediate cessation of oscillations, an inhibition time that linearly depends on the concentration of the antioxidant added, and subsequent regeneration of oscillations. Here the effects of ten antioxidants (pyrocatechol (=benzene-1,2-diol), ferulic acid (=3-(4-hydroxy-3-methoxyphenyl)prop-2-enoic acid), caffeic acid (=3-(3,4-dihydroxyphenyl)prop-2-enoic acid), 2,6-, 3,4-, 2,4-, 3,5-, and 2,5-dihydroxybenzoic acids, homovanillic acid (=4-hydroxy-3-methoxybenzeneacetic acid), and resorcinol (=benzene-1,3-diol)) were studied in detail. Relative antioxidant activities of these substances with respect to resorcinol were determined in different ways on the basis of inhibition times. The limits of the calculated values of relative activity based on the Briggs-Rauscher reaction are the same as those obtained with other analytical procedures and are discussed here. The new method is inexpensive: reagents and apparatus are commonly used in all chemical laboratories. The thermochemical behavior of the Briggs-Rauscher reaction and the dependence of inhibition time on the temperature were also carefully investigated and taken into account. A semiquantitative mechanistic interpretation of the inhibitory effects based on a suitable kinetic model is given.

Studies on the Bacillus sphaericus larvicidal activity against malarial vector species in Amazonia.

In this work, bioassays were carried out in laboratory conditions (average temperature 26 +/- 2 degrees C) to test ten strains of Bacillus sphaericus, isolated from Brazilian soils against third instar larvae from anopheline species recorded as malaria vectors in Amazonian-Anopheles nuneztovari and An. darlingi. With the former mosquito, three strains--S2, S20 and S46 showed relative activity, in 24 and 48 hr exposure to the B. spahericus strains. With the latter only the S2 and S20 were effective in the 48 hr reading. The studied strains that showed the most adequate response in the Amazonian region were S2 and S20 showing broader and more efficient results. Therefore, S2 was the most effective when the 24 and 48 hr readings were considered, because it showed the greatest relative activity values.

Structure-activity relationships of neuromedin U. II. Highly potent analogs substituted or modified at the N-terminus of neuromedin U-8.

To develop a highly potent agonist and to examine the structure-contractile activity relationship of neuromedin U-8(NMU-8), seventeen analogs were synthesized and tested for contractile activity on isolated chicken crop smooth muscle preparations. The analogs were designed to examine the contributions of cyclic structure and acidic function at the N-terminal of NMU-8 and NMU-8(2--8) to the biological activity. The relative activity (RA) values of NMU-8 analogs were as follows: [Dp-Glu1]-NMU-8,5.50; [pyrohomoglutamyl(pHgu)1]-NMU-8,4.65;[D-pHgu1]-NMU-8, 4.66; [Asp1]-NMU-8, 11.4; [acetyl(Ac)-Asp1]-NMU-8, 9.81; [Ac-Glu1]- NMU-8, 18.6; [succinyl (Suc)-Tyr1-NMU-8,69.3; [3-sulfoalanyl (Sal)1]-NMU-8, 12.7. The RA values of NMU-8(2--8) analogs were as follows: alpha-picolinyl (Pic)-NMU-8 (2--8), 7.96; 2-furoyl (Fur)-NMU-8, (2--8), 9.91; 2-thiophenecarboxyl (Thi)-NMU-8 (2--8), 3.41; 4-hydroxyphenylpropionyl (Hpp)-NMU-8(2--8), 3.20; o-phthalyl (Pht)-NMU-8 (2--8), 11.3; Suc-NMU-8 (2--8), 109; malonyl (Mlo)-NMU-8 (2--8), 17.9; maleyl (Mle)-NMU-8 (2--8), 31.6; glutaryl (Glt)-NMU-8 (2--8), 81.3; The potencies of the analogs were higher than that of p-NMU-8. Suc-NMU-8 (2--8) showed the highest potency among the analogs synthesized. The results reveal that the carboxylic acid group at the N-terminus of NMU-8 makes a major contribution to the activity.

Cytophotometry for succinate dehydrogenase activity in relation to tissue protein content with tetranitro blue tetrazolium (TNBT).

A relative cytophotometry was effectively applied for quantitative determination of succinate dehydrogenase (SDH) activity in rat liver and skeletal muscle section. The sections were stained first for SDH activity and then superimposed with protein staining by naphthol yellow S (NYS). The absorbance at 570nm and 450nm were measured cytophotometrically for the amount of TNBT-formazan and tissue protein content. The final result was expressed as a relative activity (RA) based on the ratio of the amount of TNBT-formazan to tissue protein content for the compensation of uneven section thickness. The linear relationship was obtained between the time of incubation and RA value of SDH in rat muscle section, as well as in rat liver section.In application, the present method has revealed the different frequency distribution profiles of RA of SDH in type I and II muscle fibers which were identified on the basis of the myofibrillar actomyosin ATPase activity. The RA value was less scattered in type I fiber than in type II fiber and the type II fiber could be subclassified into two groaps according to the RA-frequency profile for SDH in muscle fibers. This observation was almost in agreement with that in other studies on SDH activity-frequency profile for type II fiber.Thus, the present method was applicable to the cytophotometric determination of SDH activity in tissue sections.

Influence of processing temperature and seasonal change in diet on lipase activity and lipolysis during the mechanical separation of bovine milk

SUMMARYThe effect of separating conditions on lipase activity and free fatty acid levels in preheated milk, cream and skim milk was measured on nine occasions during a 12-week period covering the seasonal change from winter feeding to summertime grazing. This change consisted of four periods each representing a different type of forage intake, namely: silage, kale, daytime grazing and 24 h grazing. Milk was separated at 30, 40, 50 and 60°C with preheating times of 10, 25 and 55 s. Results were expressed both as absolute values and in terms of changes relative to the original unheated milk. Lipase activity and free fatty acid concentration were significantly reduced as separation temperature increased but were not influenced by holding time. The loss of activity in cream was progressive so that at 60°C only 40% of the original activity remained. Up to 50°C little change occurred in preheated milk or skim milk activity, while at 60°C 83 and 76% respectively of the original activity remained. The amount of activity calculated to be associated with the fat fraction of the cream also decreased with temperature. Activity varied significantly with date; maximum values were observed during the first 3 weeks of summertime grazing. Relative activity values indicated that the susceptibility of milk lipase to heat inactivation also varied with date. Lipolysis was also significantly affected by date. Cream free fatty acid levels were lower during the period of daytime grazing and were significantly higher than those in preheated milk. The correlation between lipase activity and free fatty acid levels was generally poor, accounting for between 0 and 34% of the variance. Possible reasons for the effect of separating temperature on lipolysis in cream are discussed.